2.1 Built-in Functions
The Python interpreter has a number of functions built into it that are always available.
They are listed here in alphabetical order.
| __import__( |
name[, globals[, locals[,
fromlist]]]) |
- This function is invoked by the import
statement. It mainly exists so that you can replace it with another function that has
a compatible interface, in order to change the semantics of the import
statement. For examples of why and how you would do this, see the standard library modules
ihooks
and rexec
. See also the built-in module imp
, which defines some useful operations out of which you can build your own __import__() function.
For example, the statement "import spam" results in the
following call: __import__('spam', globals(), locals(),
[]); the statement "from spam.ham import eggs"
results in "__import__('spam.ham', globals(), locals(), ['eggs'])".
Note that even though locals() and ['eggs'] are passed in as
arguments, the __import__() function does not set the local
variable named eggs; this is done by subsequent code that is generated for
the import statement. (In fact, the standard implementation does not use its locals
argument at all, and uses its globals only to determine the package context of
the import statement.)
When the name variable is of the form package.module, normally,
the top-level package (the name up till the first dot) is returned, not the module
named by name. However, when a non-empty fromlist argument is given,
the module named by name is returned. This is done for compatibility with the
bytecode generated for the different kinds of import statement; when using "import spam.ham.eggs", the top-level package spam
must be placed in the importing namespace, but when using "from
spam.ham import eggs", the spam.ham subpackage must be used to find
the eggs variable. As a workaround for this behavior, use getattr() to extract the desired components. For example, you could
define the following helper:
def my_import(name):
mod = __import__(name)
components = name.split('.')
for comp in components[1:]:
mod = getattr(mod, comp)
return mod
-
- Return the absolute value of a number. The argument may be a plain or long integer or a
floating point number. If the argument is a complex number, its magnitude is returned.
-
- This abstract type is the superclass for str and unicode. It cannot be called or instantiated, but it can be used to
test whether an object is an instance of str or unicode.
isinstance(obj, basestring) is equivalent to isinstance(obj, (str,
unicode)). New in version 2.3.
-
- Convert a value to a Boolean, using the standard truth testing procedure. If x
is false or omitted, this returns False; otherwise it returns True. bool is also a class, which is a
subclass of int. Class bool cannot be
subclassed further. Its only instances are False and True.
New in version 2.2.1. Changed
in version 2.3: If no argument is given, this function returns False.
-
- Return true if the object argument appears callable, false if not. If this
returns true, it is still possible that a call fails, but if it is false, calling object
will never succeed. Note that classes are callable (calling a class returns a new
instance); class instances are callable if they have a __call__()
method.
-
- Return a string of one character whose ASCII code is the integer i. For
example,
chr(97) returns the string 'a'. This is the inverse of ord(). The argument must be in the range [0..255], inclusive; ValueError will be raised if i is outside that range.
-
- Return a class method for function.
A class method receives the class as implicit first argument, just like an instance
method receives the instance. To declare a class method, use this idiom:
class C:
def f(cls, arg1, arg2, ...): ...
f = classmethod(f)
It can be called either on the class (such as C.f()) or on an instance
(such as C().f()). The instance is ignored except for its class. If a class
method is called for a derived class, the derived class object is passed as the implied
first argument.
Class methods are different than C++ or Java static methods. If you want those, see staticmethod() in this section. New in
version 2.2.
-
- Compare the two objects x and y and return an integer according to
the outcome. The return value is negative if
x < y,
zero if x == y and strictly positive if x
> y.
-
| compile( |
string, filename, kind[, flags[,
dont_inherit]]) |
- Compile the string into a code object. Code objects can be executed by an exec statement or evaluated by a call to eval().
The filename argument should give the file from which the code was read; pass
some recognizable value if it wasn't read from a file (
'<string>' is
commonly used). The kind argument specifies what kind of code must be compiled;
it can be 'exec' if string consists of a sequence of statements, 'eval'
if it consists of a single expression, or 'single' if it consists of a single
interactive statement (in the latter case, expression statements that evaluate to
something else than None will printed).
When compiling multi-line statements, two caveats apply: line endings must be
represented by a single newline character ('\n'), and the input must be
terminated by at least one newline character. If line endings are represented by '\r\n',
use the string replace() method to change them into '\n'.
The optional arguments flags and dont_inherit (which are new in
Python 2.2) control which future statements (see PEP 236) affect the compilation of string.
If neither is present (or both are zero) the code is compiled with those future statements
that are in effect in the code that is calling compile. If the flags argument
is given and dont_inherit is not (or is zero) then the future statements
specified by the flags argument are used in addition to those that would be
used anyway. If dont_inherit is a non-zero integer then the flags
argument is it - the future statements in effect around the call to compile are ignored.
Future statemants are specified by bits which can be bitwise or-ed together to specify
multiple statements. The bitfield required to specify a given feature can be found as the compiler_flag attribute on the _Feature
instance in the __future__ module.
-
- Create a complex number with the value real + imag*j or convert a
string or number to a complex number. If the first parameter is a string, it will be
interpreted as a complex number and the function must be called without a second
parameter. The second parameter can never be a string. Each argument may be any numeric
type (including complex). If imag is omitted, it defaults to zero and the
function serves as a numeric conversion function like int(), long() and float(). If both arguments are
omitted, returns
0j.
-
- This is a relative of setattr(). The arguments are an object
and a string. The string must be the name of one of the object's attributes. The function
deletes the named attribute, provided the object allows it. For example,
delattr(x,
'foobar') is equivalent to del x.foobar.
-
| dict( |
[mapping-or-sequence]) |
- Return a new dictionary initialized from an optional positional argument or from a set
of keyword arguments. If no arguments are given, return a new empty dictionary. If the
positional argument is a mapping object, return a dictionary mapping the same keys to the
same values as does the mapping object. Otherwise the positional argument must be a
sequence, a container that supports iteration, or an iterator object. The elements of the
argument must each also be of one of those kinds, and each must in turn contain exactly
two objects. The first is used as a key in the new dictionary, and the second as the key's
value. If a given key is seen more than once, the last value associated with it is
retained in the new dictionary.
If keyword arguments are given, the keywords themselves with their associated values
are added as items to the dictionary. If a key is specified both in the positional
argument and as a keyword argument, the value associated with the keyword is retained in
the dictionary. For example, these all return a dictionary equal to {"one":
2, "two": 3}:
dict({'one': 2, 'two': 3})dict({'one': 2, 'two': 3}.items())dict({'one': 2, 'two': 3}.iteritems())dict(zip(('one', 'two'), (2, 3)))dict([['two', 3], ['one', 2]])dict(one=2, two=3)dict([(['one', 'two'][i-2], i) for i in (2, 3)])
New in version 2.2. Changed
in version 2.3: Support for building a dictionary from keyword arguments added.
-
- Without arguments, return the list of names in the current local symbol table. With an
argument, attempts to return a list of valid attributes for that object. This information
is gleaned from the object's __dict__ attribute, if defined, and
from the class or type object. The list is not necessarily complete. If the object is a
module object, the list contains the names of the module's attributes. If the object is a
type or class object, the list contains the names of its attributes, and recursively of
the attributes of its bases. Otherwise, the list contains the object's attributes' names,
the names of its class's attributes, and recursively of the attributes of its class's base
classes. The resulting list is sorted alphabetically. For example:
>>> import struct
>>> dir()
['__builtins__', '__doc__', '__name__', 'struct']
>>> dir(struct)
['__doc__', '__name__', 'calcsize', 'error', 'pack', 'unpack']
Note: Because dir()
is supplied primarily as a convenience for use at an interactive prompt, it tries to
supply an interesting set of names more than it tries to supply a rigorously or
consistently defined set of names, and its detailed behavior may change across releases.
-
- Take two (non complex) numbers as arguments and return a pair of numbers consisting of
their quotient and remainder when using long division. With mixed operand types, the rules
for binary arithmetic operators apply. For plain and long integers, the result is the same
as
(a / b, a % b). For floating
point numbers the result is (q, a % b),
where q is usually math.floor(a / b) but may
be 1 less than that. In any case q * b + a % b
is very close to a, if a % b is non-zero it
has the same sign as b, and 0 <= abs(a % b) <
abs(b).
Changed in version 2.3: Using divmod()
with complex numbers is deprecated.
-
- Return an enumerate object. iterable must be a sequence, an iterator, or some
other object which supports iteration. The next() method of the
iterator returned by enumerate() returns a tuple containing a
count (from zero) and the corresponding value obtained from iterating over iterable.
enumerate() is useful for obtaining an indexed series:
(0,
seq[0]), (1, seq[1]), (2, seq[2]), .... New in version 2.3.
-
| eval( |
expression[, globals[, locals]]) |
- The arguments are a string and two optional dictionaries. The expression
argument is parsed and evaluated as a Python expression (technically speaking, a condition
list) using the globals and locals dictionaries as global and local
name space. If the globals dictionary is present and lacks '__builtins__', the
current globals are copied into globals before expression is parsed.
This means that expression normally has full access to the standard __builtin__ module and restricted
environments are propagated. If the locals dictionary is omitted it defaults to
the globals dictionary. If both dictionaries are omitted, the expression is
executed in the environment where eval is called. The return
value is the result of the evaluated expression. Syntax errors are reported as exceptions.
Example:
>>> x = 1
>>> print eval('x+1')
2
This function can also be used to execute arbitrary code objects (such as those created
by compile()). In this case pass a code object instead of a
string. The code object must have been compiled passing 'eval' as the kind
argument.
Hints: dynamic execution of statements is supported by the exec
statement. Execution of statements from a file is supported by the execfile()
function. The globals() and locals()
functions returns the current global and local dictionary, respectively, which may be
useful to pass around for use by eval() or execfile().
-
| execfile( |
filename[, globals[, locals]]) |
- This function is similar to the exec statement, but parses a
file instead of a string. It is different from the import
statement in that it does not use the module administration -- it reads the file
unconditionally and does not create a new module.2.2
The arguments are a file name and two optional dictionaries. The file is parsed and
evaluated as a sequence of Python statements (similarly to a module) using the globals
and locals dictionaries as global and local namespace. If the locals
dictionary is omitted it defaults to the globals dictionary. If both
dictionaries are omitted, the expression is executed in the environment where execfile() is called. The return value is None.
Warning: The default locals act
as described for function locals() below: modifications to the
default locals dictionary should not be attempted. Pass an explicit locals
dictionary if you need to see effects of the code on locals after function execfile() returns. execfile() cannot be
used reliably to modify a function's locals.
-
| file( |
filename[, mode[, bufsize]]) |
- Return a new file object (described earlier under Built-in Types). The first two
arguments are the same as for
stdio's fopen(): filename
is the file name to be opened, mode indicates how the file is to be opened: 'r'
for reading, 'w' for writing (truncating an existing file), and 'a'
opens it for appending (which on some Unix
systems means that all writes append to the end of the file, regardless of the
current seek position).
Modes 'r+', 'w+' and 'a+' open the file for
updating (note that 'w+' truncates the file). Append 'b' to the
mode to open the file in binary mode, on systems that differentiate between binary and
text files (else it is ignored). If the file cannot be opened, IOError
is raised.
In addition to the standard fopen() values mode
may be 'U' or 'rU'. If Python is built with universal newline
support (the default) the file is opened as a text file, but lines may be terminated by
any of '\n', the Unix end-of-line convention, '\r', the
Macintosh convention or '\r\n', the Windows convention. All of these external
representations are seen as '\n' by the Python program. If Python is built
without universal newline support mode 'U' is the same as normal
text mode. Note that file objects so opened also have an attribute called newlines which has a value of None (if no newlines have
yet been seen), '\n', '\r', '\r\n', or a tuple
containing all the newline types seen.
If mode is omitted, it defaults to 'r'. When opening a binary
file, you should append 'b' to the mode value for improved
portability. (It's useful even on systems which don't treat binary and text files
differently, where it serves as documentation.)
The optional bufsize argument specifies the file's desired buffer size: 0
means unbuffered, 1 means line buffered, any other positive value means use a buffer of
(approximately) that size. A negative bufsize means to use the system default,
which is usually line buffered for tty devices and fully buffered for other files. If
omitted, the system default is used.2.3
The file() constructor is new in Python 2.2. The previous
spelling, open(), is retained for compatibility, and is an alias
for file().
-
- Construct a list from those elements of list for which function
returns true. list may be either a sequence, a container which supports
iteration, or an iterator, If list is a string or a tuple, the result also has
that type; otherwise it is always a list. If function is
None, the
identity function is assumed, that is, all elements of list that are false
(zero or empty) are removed.
Note that filter(function, list) is equivalent to [item
for item in list if function(item)] if function is not None
and [item for item in list if item] if function is None.
-
- Convert a string or a number to floating point. If the argument is a string, it must
contain a possibly signed decimal or floating point number, possibly embedded in
whitespace; this behaves identical to
string.atof(x). Otherwise,
the argument may be a plain or long integer or a floating point number, and a floating
point number with the same value (within Python's floating point precision) is returned.
If no argument is given, returns 0.0.
Note: When passing in a string, values for NaN
and Infinity
may be returned, depending on the underlying C library. The specific set of strings
accepted which cause these values to be returned depends entirely on the C library and is
known to vary.
-
| getattr( |
object, name[, default]) |
- Return the value of the named attributed of object. name must be a
string. If the string is the name of one of the object's attributes, the result is the
value of that attribute. For example,
getattr(x, 'foobar') is equivalent to x.foobar.
If the named attribute does not exist, default is returned if provided,
otherwise AttributeError is raised.
-
- Return a dictionary representing the current global symbol table. This is always the
dictionary of the current module (inside a function or method, this is the module where it
is defined, not the module from which it is called).
-
- The arguments are an object and a string. The result is 1 if the string is the name of
one of the object's attributes, 0 if not. (This is implemented by calling
getattr(object,
name) and seeing whether it raises an exception or not.)
-
- Return the hash value of the object (if it has one). Hash values are integers. They are
used to quickly compare dictionary keys during a dictionary lookup. Numeric values that
compare equal have the same hash value (even if they are of different types, as is the
case for 1 and 1.0).
-
- Invoke the built-in help system. (This function is intended for interactive use.) If no
argument is given, the interactive help system starts on the interpreter console. If the
argument is a string, then the string is looked up as the name of a module, function,
class, method, keyword, or documentation topic, and a help page is printed on the console.
If the argument is any other kind of object, a help page on the object is generated. New in version 2.2.
-
- Convert an integer number (of any size) to a hexadecimal string. The result is a valid
Python expression. Note: this always yields an unsigned literal. For example, on a 32-bit
machine,
hex(-1) yields '0xffffffff'. When evaluated on a
machine with the same word size, this literal is evaluated as -1; at a different word
size, it may turn up as a large positive number or raise an OverflowError
exception.
-
- Return the `identity' of an object. This is an integer (or long integer) which is
guaranteed to be unique and constant for this object during its lifetime. Two objects
whose lifetimes are disjunct may have the same id() value.
(Implementation note: this is the address of the object.)
-
- Equivalent to
eval(raw_input(prompt)). Warning: This function is not safe from user errors! It expects a valid
Python expression as input; if the input is not syntactically valid, a SyntaxError will be raised. Other exceptions may be raised if there
is an error during evaluation. (On the other hand, sometimes this is exactly what you need
when writing a quick script for expert use.)
If the readline module was
loaded, then input() will use it to provide elaborate line
editing and history features.
Consider using the raw_input() function for general input
from users.
-
- Convert a string or number to a plain integer. If the argument is a string, it must
contain a possibly signed decimal number representable as a Python integer, possibly
embedded in whitespace. The radix parameter gives the base for the conversion
and may be any integer in the range [2, 36], or zero. If radix is zero, the
proper radix is guessed based on the contents of string; the interpretation is the same as
for integer literals. If radix is specified and x is not a string, TypeError is raised. Otherwise, the argument may be a plain or long
integer or a floating point number. Conversion of floating point numbers to integers
truncates (towards zero). If the argument is outside the integer range a long object will
be returned instead. If no arguments are given, returns
0.
-
| isinstance( |
object, classinfo) |
- Return true if the object argument is an instance of the classinfo
argument, or of a (direct or indirect) subclass thereof. Also return true if classinfo
is a type object and object is an object of that type. If object is
not a class instance or an object of the given type, the function always returns false. If
classinfo is neither a class object nor a type object, it may be a tuple of
class or type objects, or may recursively contain other such tuples (other sequence types
are not accepted). If classinfo is not a class, type, or tuple of classes,
types, and such tuples, a TypeError exception is raised. Changed in version 2.2: Support for a tuple of type information was
added.
-
| issubclass( |
class, classinfo) |
- Return true if class is a subclass (direct or indirect) of classinfo.
A class is considered a subclass of itself. classinfo may be a tuple of class
objects, in which case every entry in classinfo will be checked. In any other
case, a TypeError exception is raised. Changed in version 2.3: Support for a tuple of type information was
added.
-
- Return an iterator object. The first argument is interpreted very differently depending
on the presence of the second argument. Without a second argument, o must be a
collection object which supports the iteration protocol (the __iter__()
method), or it must support the sequence protocol (the __getitem__()
method with integer arguments starting at
0). If it does not support either
of those protocols, TypeError is raised. If the second
argument, sentinel, is given, then o must be a callable object. The
iterator created in this case will call o with no arguments for each call to
its next() method; if the value returned is equal to sentinel,
StopIteration will be raised, otherwise the value will be
returned. New in version 2.2.
-
- Return the length (the number of items) of an object. The argument may be a sequence
(string, tuple or list) or a mapping (dictionary).
-
- Return a list whose items are the same and in the same order as sequence's
items. sequence may be either a sequence, a container that supports iteration,
or an iterator object. If sequence is already a list, a copy is made and
returned, similar to
sequence[:]. For instance, list('abc')
returns ['a', 'b', 'c'] and list( (1, 2, 3) ) returns [1,
2, 3]. If no argument is given, returns a new empty list, [].
-
- Update and return a dictionary representing the current local symbol table. Warning: The contents of this dictionary should not
be modified; changes may not affect the values of local variables used by the interpreter.
-
- Convert a string or number to a long integer. If the argument is a string, it must
contain a possibly signed number of arbitrary size, possibly embedded in whitespace; this
behaves identical to
string.atol(x). The radix argument
is interpreted in the same way as for int(), and may only be
given when x is a string. Otherwise, the argument may be a plain or long
integer or a floating point number, and a long integer with the same value is returned.
Conversion of floating point numbers to integers truncates (towards zero). If no arguments
are given, returns 0L.
-
| map( |
function, list, ...) |
- Apply function to every item of list and return a list of the
results. If additional list arguments are passed, function must take
that many arguments and is applied to the items of all lists in parallel; if a list is
shorter than another it is assumed to be extended with
None items. If function
is None, the identity function is assumed; if there are multiple list
arguments, map() returns a list consisting of tuples containing
the corresponding items from all lists (a kind of transpose operation). The list
arguments may be any kind of sequence; the result is always a list.
-
- With a single argument s, return the largest item of a non-empty sequence
(such as a string, tuple or list). With more than one argument, return the largest of the
arguments.
-
- With a single argument s, return the smallest item of a non-empty sequence
(such as a string, tuple or list). With more than one argument, return the smallest of the
arguments.
-
- Return a new featureless object. object() is a base for all
new style classes. It has the methods that are common to all instances of new style
classes. New in version 2.2.
Changed in version 2.3: This function does not accept any
arguments. Formerly, it accepted arguments but ignored them.
-
- Convert an integer number (of any size) to an octal string. The result is a valid Python
expression. Note: this always yields an unsigned literal. For example, on a 32-bit
machine,
oct(-1) yields '037777777777'. When evaluated on a
machine with the same word size, this literal is evaluated as -1; at a different word
size, it may turn up as a large positive number or raise an OverflowError
exception.
-
| open( |
filename[, mode[, bufsize]]) |
- An alias for the file() function above.
-
- Return the ASCII value of a string of one character or a Unicode character. E.g.,
ord('a')
returns the integer 97, ord(u'\u2020') returns 8224.
This is the inverse of chr() for strings and of unichr() for Unicode characters.
-
- Return x to the power y; if z is present, return x
to the power y, modulo z (computed more efficiently than
pow(x,
y) % z). The arguments must have numeric types. With mixed
operand types, the coercion rules for binary arithmetic operators apply. For int and long
int operands, the result has the same type as the operands (after coercion) unless the
second argument is negative; in that case, all arguments are converted to float and a
float result is delivered. For example, 10**2 returns 100, but 10**-2
returns 0.01. (This last feature was added in Python 2.2. In Python 2.1 and
before, if both arguments were of integer types and the second argument was negative, an
exception was raised.) If the second argument is negative, the third argument must be
omitted. If z is present, x and y must be of integer
types, and y must be non-negative. (This restriction was added in Python 2.2.
In Python 2.1 and before, floating 3-argument pow() returned
platform-dependent results depending on floating-point rounding accidents.)
-
| property( |
[fget[, fset[, fdel[,
doc]]]]) |
- Return a property attribute for new-style classes (classes that derive from object).
fget is a function for getting an attribute value, likewise fset
is a function for setting, and fdel a function for del'ing, an attribute.
Typical use is to define a managed attribute x:
class C(object):
def getx(self): return self.__x
def setx(self, value): self.__x = value
def delx(self): del self.__x
x = property(getx, setx, delx, "I'm the 'x' property.")
New in version 2.2.
-
| range( |
[start,] stop[, step]) |
- This is a versatile function to create lists containing arithmetic progressions. It is
most often used in for loops. The arguments must be plain
integers. If the step argument is omitted, it defaults to
1. If
the start argument is omitted, it defaults to 0. The full form
returns a list of plain integers [start, start + step,
start + 2 * step, ...]. If step is positive, the
last element is the largest start + i * step
less than stop; if step is negative, the last element is the largest
start + i * step greater than stop.
step must not be zero (or else ValueError is
raised). Example:
>>> range(10)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> range(1, 11)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
>>> range(0, 30, 5)
[0, 5, 10, 15, 20, 25]
>>> range(0, 10, 3)
[0, 3, 6, 9]
>>> range(0, -10, -1)
[0, -1, -2, -3, -4, -5, -6, -7, -8, -9]
>>> range(0)
[]
>>> range(1, 0)
[]
-
- If the prompt argument is present, it is written to standard output without a
trailing newline. The function then reads a line from input, converts it to a string
(stripping a trailing newline), and returns that. When EOF is read, EOFError
is raised. Example:
>>> s = raw_input('--> ')
--> Monty Python's Flying Circus
>>> s
"Monty Python's Flying Circus"
If the readline module was
loaded, then raw_input() will use it to provide elaborate line
editing and history features.
-
| reduce( |
function, sequence[, initializer]) |
- Apply function of two arguments cumulatively to the items of sequence,
from left to right, so as to reduce the sequence to a single value. For example,
reduce(lambda
x, y: x+y, [1, 2, 3, 4, 5]) calculates ((((1+2)+3)+4)+5). The left
argument, x, is the accumulated value and the right argument, y, is
the update value from the sequence. If the optional initializer is
present, it is placed before the items of the sequence in the calculation, and serves as a
default when the sequence is empty. If initializer is not given and sequence
contains only one item, the first item is returned.
-
- Re-parse and re-initialize an already imported module. The argument must be a
module object, so it must have been successfully imported before. This is useful if you
have edited the module source file using an external editor and want to try out the new
version without leaving the Python interpreter. The return value is the module object (the
same as the module argument).
There are a number of caveats:
If a module is syntactically correct but its initialization fails, the first import statement for it does not bind its name locally, but does
store a (partially initialized) module object in sys.modules. To reload the
module you must first import it again (this will bind the name to
the partially initialized module object) before you can reload()
it.
When a module is reloaded, its dictionary (containing the module's global variables) is
retained. Redefinitions of names will override the old definitions, so this is generally
not a problem. If the new version of a module does not define a name that was defined by
the old version, the old definition remains. This feature can be used to the module's
advantage if it maintains a global table or cache of objects -- with a try
statement it can test for the table's presence and skip its initialization if desired.
It is legal though generally not very useful to reload built-in or dynamically loaded
modules, except for sys, __main__ and __builtin__. In many cases, however, extension modules
are not designed to be initialized more than once, and may fail in arbitrary ways when
reloaded.
If a module imports objects from another module using from ...
import ..., calling reload() for the
other module does not redefine the objects imported from it -- one way around this is to
re-execute the from statement, another is to use import and qualified names (module.name)
instead.
If a module instantiates instances of a class, reloading the module that defines the
class does not affect the method definitions of the instances -- they continue to use the
old class definition. The same is true for derived classes.
-
- Return a string containing a printable representation of an object. This is the same
value yielded by conversions (reverse quotes). It is sometimes useful to be able to access
this operation as an ordinary function. For many types, this function makes an attempt to
return a string that would yield an object with the same value when passed to eval().
-
- Return the floating point value x rounded to n digits after the
decimal point. If n is omitted, it defaults to zero. The result is a floating
point number. Values are rounded to the closest multiple of 10 to the power minus n;
if two multiples are equally close, rounding is done away from 0 (so. for example,
round(0.5)
is 1.0 and round(-0.5) is -1.0).
-
| setattr( |
object, name, value) |
- This is the counterpart of getattr(). The arguments are an
object, a string and an arbitrary value. The string may name an existing attribute or a
new attribute. The function assigns the value to the attribute, provided the object allows
it. For example,
setattr(x, 'foobar', 123) is
equivalent to x.foobar = 123.
-
| slice( |
[start,] stop[, step]) |
- Return a slice object representing the set of indices specified by
range(start,
stop, step). The start and step
arguments default to None. Slice objects have read-only data attributes start, stop and step
which merely return the argument values (or their default). They have no other explicit
functionality; however they are used by Numerical Python
and other third party extensions. Slice objects are also generated when extended
indexing syntax is used. For example: "a[start:stop:step]"
or "a[start:stop, i]".
-
- Return a static method for function.
A static method does not receive an implicit first argument. To declare a static
method, use this idiom:
class C:
def f(arg1, arg2, ...): ...
f = staticmethod(f)
It can be called either on the class (such as C.f()) or on an instance
(such as C().f()). The instance is ignored except for its class.
Static methods in Python are similar to those found in Java or C++. For a more advanced
concept, see classmethod() in this section. New in version 2.2.
-
- Return a string containing a nicely printable representation of an object. For strings,
this returns the string itself. The difference with
repr(object)
is that str(object) does not always attempt to return a string
that is acceptable to eval(); its goal is to return a printable
string. If no argument is given, returns the empty string, ''.
-
- Sums start and the items of a sequence, from left to right, and
returns the total. start defaults to
0. The sequence's
items are normally numbers, and are not allowed to be strings. The fast, correct way to
concatenate sequence of strings is by calling ''.join(sequence).
Note that sum(range(n), m) is equivalent to reduce(operator.add,
range(n), m) New in version 2.3.
-
| super( |
type[, object-or-type]) |
- Return the superclass of type. If the second argument is omitted the super
object returned is unbound. If the second argument is an object,
isinstance(obj,
type) must be true. If the second argument is a type, issubclass(type2,
type) must be true. super() only works for
new-style classes.
A typical use for calling a cooperative superclass method is:
class C(B):
def meth(self, arg):
super(C, self).meth(arg)
New in version 2.2.
-
- Return a tuple whose items are the same and in the same order as sequence's
items. sequence may be a sequence, a container that supports iteration, or an
iterator object. If sequence is already a tuple, it is returned unchanged. For
instance,
tuple('abc') returns ('a', 'b', 'c') and tuple([1,
2, 3]) returns (1, 2, 3). If no argument is given, returns a new empty
tuple, ().
-
- Return the type of an object. The return value is a type
object. The standard module types
defines names for all built-in types that don't already have built-in names. For
instance:
>>> import types
>>> x = 'abc'
>>> if type(x) is str: print "It's a string"
...
It's a string
>>> def f(): pass
...
>>> if type(f) is types.FunctionType: print "It's a function"
...
It's a function
The isinstance() built-in function is recommended for testing
the type of an object.
-
- Return the Unicode string of one character whose Unicode code is the integer i.
For example,
unichr(97) returns the string u'a'. This is the
inverse of ord() for Unicode strings. The argument must be in
the range [0..65535], inclusive. ValueError is raised
otherwise. New in version 2.0.
-
| unicode( |
[object[, encoding [,
errors]]]) |
- Return the Unicode string version of object using one of the following modes:
If encoding and/or errors are given, unicode() will
decode the object which can either be an 8-bit string or a character buffer using the
codec for encoding. The encoding parameter is a string giving the
name of an encoding; if the encoding is not known, LookupError
is raised. Error handling is done according to errors; this specifies the
treatment of characters which are invalid in the input encoding. If errors is 'strict'
(the default), a ValueError is raised on errors, while a value
of 'ignore' causes errors to be silently ignored, and a value of 'replace'
causes the official Unicode replacement character, U+FFFD, to be used to
replace input characters which cannot be decoded. See also the codecs module.
If no optional parameters are given, unicode() will mimic the behaviour of
str() except that it returns Unicode strings instead of 8-bit strings. More
precisely, if object is a Unicode string or subclass it will return that
Unicode string without any additional decoding applied.
For objects which provide a __unicode__() method, it will call
this method without arguments to create a Unicode string. For all other objects, the 8-bit
string version or representation is requested and then converted to a Unicode string using
the codec for the default encoding in 'strict' mode.
New in version 2.0. Changed
in version 2.2: Support for __unicode__() added.
-
- Without arguments, return a dictionary corresponding to the current local symbol table.
With a module, class or class instance object as argument (or anything else that has a __dict__ attribute), returns a dictionary corresponding to the
object's symbol table. The returned dictionary should not be modified: the effects on the
corresponding symbol table are undefined.2.4
-
| xrange( |
[start,] stop[, step]) |
- This function is very similar to range(), but returns an ``xrange
object'' instead of a list. This is an opaque sequence type which yields the same values
as the corresponding list, without actually storing them all simultaneously. The advantage
of xrange() over range() is minimal
(since xrange() still has to create the values when asked for
them) except when a very large range is used on a memory-starved machine or when all of
the range's elements are never used (such as when the loop is usually terminated with break).
-
- This function returns a list of tuples, where the i-th tuple contains the i-th
element from each of the argument sequences. At least one sequence is required, otherwise
a TypeError is raised. The returned list is truncated in length
to the length of the shortest argument sequence. When there are multiple argument
sequences which are all of the same length, zip() is similar to map() with an initial argument of
None. With a single
sequence argument, it returns a list of 1-tuples. New in version
2.0.
|
