9.1 Debugger Commands
The debugger recognizes the following commands. Most commands can be abbreviated to one or
two letters; e.g. "h(elp)" means that either "h" or "help" can be used to enter the
help command (but not "he" or "hel",
nor "H" or "Help" or "HELP"). Arguments to commands must be separated by whitespace (spaces
or tabs). Optional arguments are enclosed in square brackets ("")
in the command syntax; the square brackets must not be typed. Alternatives in the command
syntax are separated by a vertical bar ("|").
Entering a blank line repeats the last command entered. Exception: if the last command was
a "list" command, the next 11 lines are listed.
Commands that the debugger doesn't recognize are assumed to be Python statements and are
executed in the context of the program being debugged. Python statements can also be prefixed
with an exclamation point ("!"). This is a powerful way to
inspect the program being debugged; it is even possible to change a variable or call a
function. When an exception occurs in such a statement, the exception name is printed but the
debugger's state is not changed.
Multiple commands may be entered on a single line, separated by ";;".
(A single ";" is not used as it is the separator for multiple
commands in a line that is passed to the Python parser.) No intelligence is applied to
separating the commands; the input is split at the first ";;"
pair, even if it is in the middle of a quoted string.
The debugger supports aliases. Aliases can have parameters which allows one a certain level
of adaptability to the context under examination.
If a file .pdbrc
exists in the user's home directory or in the current directory, it is read in and
executed as if it had been typed at the debugger prompt. This is particularly useful for
aliases. If both files exist, the one in the home directory is read first and aliases defined
there can be overridden by the local file.
- h(elp) [command]
Without argument, print the list of available commands. With a command as
argument, print help about that command. "help pdb"
displays the full documentation file; if the environment variable PAGER is defined, the file is piped through that command instead. Since
the command argument must be an identifier, "help exec"
must be entered to get help on the "!" command.
Print a stack trace, with the most recent frame at the bottom. An arrow indicates the
current frame, which determines the context of most commands.
Move the current frame one level down in the stack trace (to an newer frame).
Move the current frame one level up in the stack trace (to a older frame).
- b(reak) [[filename:]lineno
With a lineno argument, set a break there in the current file. With a function
argument, set a break at the first executable statement within that function. The line
number may be prefixed with a filename and a colon, to specify a breakpoint in another
file (probably one that hasn't been loaded yet). The file is searched on
Note that each breakpoint is assigned a number to which all the other breakpoint commands
If a second argument is present, it is an expression which must evaluate to true before
the breakpoint is honored.
Without argument, list all breaks, including for each breakpoint, the number of times
that breakpoint has been hit, the current ignore count, and the associated condition if
- tbreak [[filename:]lineno
Temporary breakpoint, which is removed automatically when it is first hit. The
arguments are the same as break.
- cl(ear) [bpnumber [bpnumber ...]]
With a space separated list of breakpoint numbers, clear those breakpoints. Without
argument, clear all breaks (but first ask confirmation).
- disable [bpnumber [bpnumber ...]]
Disables the breakpoints given as a space separated list of breakpoint numbers.
Disabling a breakpoint means it cannot cause the program to stop execution, but unlike
clearing a breakpoint, it remains in the list of breakpoints and can be (re-)enabled.
- enable [bpnumber [bpnumber ...]]
Enables the breakpoints specified.
- ignore bpnumber [count]
Sets the ignore count for the given breakpoint number. If count is omitted, the ignore
count is set to 0. A breakpoint becomes active when the ignore count is zero. When
non-zero, the count is decremented each time the breakpoint is reached and the breakpoint
is not disabled and any associated condition evaluates to true.
- condition bpnumber [condition]
Condition is an expression which must evaluate to true before the breakpoint is
honored. If condition is absent, any existing condition is removed; i.e., the breakpoint
is made unconditional.
Execute the current line, stop at the first possible occasion (either in a function
that is called or on the next line in the current function).
Continue execution until the next line in the current function is reached or it
returns. (The difference between "next" and "step" is that "step" stops inside a
called function, while "next" executes called functions at
(nearly) full speed, only stopping at the next line in the current function.)
Continue execution until the current function returns.
Continue execution, only stop when a breakpoint is encountered.
- j(ump) lineno
Set the next line that will be executed. Only available in the bottom-most frame. This
lets you jump back and execute code again, or jump forward to skip code that you don't
want to run.
It should be noted that not all jumps are allowed -- for instance it is not possible to
jump into the middle of a for loop or out of a finally clause.
- l(ist) [first[, last]]
List source code for the current file. Without arguments, list 11 lines around the
current line or continue the previous listing. With one argument, list 11 lines around at
that line. With two arguments, list the given range; if the second argument is less than
the first, it is interpreted as a count.
Print the argument list of the current function.
- p expression
Evaluate the expression in the current context and print its value. Note: "print" can also
be used, but is not a debugger command -- this executes the Python print
- pp expression
Like the "p" command, except the value of the exception
is pretty-printed using the pprint module.
- alias [name [command]]
Creates an alias called name that executes command. The command
must not be enclosed in quotes. Replaceable parameters can be indicated by "%1", "%2", and so on, while "%*" is replaced by all the parameters. If no command is given, the
current alias for name is shown. If no arguments are given, all aliases are
Aliases may be nested and can contain anything that can be legally typed at the pdb
prompt. Note that internal pdb commands can be overridden by aliases. Such a
command is then hidden until the alias is removed. Aliasing is recursively applied to the
first word of the command line; all other words in the line are left alone.
As an example, here are two useful aliases (especially when placed in the .pdbrc file):
#Print instance variables (usage "pi classInst")
alias pi for k in %1.__dict__.keys(): print "%1.",k,"=",%1.__dict__[k]
#Print instance variables in self
alias ps pi self
- unalias name
Deletes the specified alias.
Execute the (one-line) statement in the context of the current stack frame.
The exclamation point can be omitted unless the first word of the statement resembles a
debugger command. To set a global variable, you can prefix the assignment command with a
"global" command on the same line, e.g.:
(Pdb) global list_options; list_options = ['-l']
Quit from the debugger. The program being executed is aborted.