Debugger Commands¶

The commands recognized by the debugger are listed below. Most commands can beabbreviated to one or two letters as indicated; e.g.h(elp) means thateitherh orhelp can be used to enter the help command (but notheorhel, norH orHelp orHELP). Arguments to commands must beseparated by whitespace (spaces or tabs). Optional arguments are enclosed insquare brackets ([]) in the command syntax; the square brackets must not betyped. Alternatives in the command syntax are separated by a vertical bar(|).

Entering a blank line repeats the last command entered. Exception: if the lastcommand was alist command, the next 11 lines are listed.

Commands that the debugger doesn’t recognize are assumed to be Python statementsand are executed in the context of the program being debugged. Pythonstatements can also be prefixed with an exclamation point (!). This is apowerful way to inspect the program being debugged; it is even possible tochange a variable or call a function. When an exception occurs in such astatement, the exception name is printed but the debugger’s state is notchanged.

The debugger supportsaliases. Aliases can haveparameters which allows one a certain level of adaptability to the context underexamination.

Multiple commands may be entered on a single line, separated by;;. (Asingle; is not used as it is the separator for multiple commands in a linethat is passed to the Python parser.) No intelligence is applied to separatingthe commands; the input is split at the first;; pair, even if it is in themiddle of a quoted string. A workaround for strings with double semicolonsis to use implicit string concatenation';'';' or";"";".

To set a temporary global variable, use aconvenience variable. Aconveniencevariable is a variable whose name starts with$. For example,$foo=1sets a global variable$foo which you can use in the debugger session. Theconvenience variables are cleared when the program resumes execution so it’sless likely to interfere with your program compared to using normal variableslikefoo=1.

There are four presetconvenience variables:

• $_frame: the current frame you are debugging

• $_retval: the return value if the frame is returning

• $_exception: the exception if the frame is raising an exception

• $_asynctask: the asyncio task if pdb stops in an async function

If a file.pdbrc exists in the user’s home directory or in the currentdirectory, it is read with'utf-8' encoding and executed as if it had beentyped at the debugger prompt, with the exception that empty lines and linesstarting with# are ignored. This is particularly useful for aliases. If bothfiles exist, the one in the home directory is read first and aliases defined therecan be overridden by the local file.

h(elp)[command]¶

Without argument, print the list of available commands. With acommand asargument, print help about that command.helppdb displays the fulldocumentation (the docstring of thepdb module). Since thecommandargument must be an identifier,helpexec must be entered to get help onthe! command.

w(here)[count]¶

Print a stack trace, with the most recent frame at the bottom. ifcountis 0, print the current frame entry. Ifcount is negative, print the leastrecent -count frames. Ifcount is positive, print the most recentcount frames. An arrow (>)indicates the current frame, which determines the context of most commands.

Changed in version 3.14:count argument is added.

d(own)[count]¶

Move the current framecount (default one) levels down in the stack trace(to a newer frame).

u(p)[count]¶

Move the current framecount (default one) levels up in the stack trace (toan older frame).

b(reak)[([filename:]lineno|function)[,condition]]¶

With alineno argument, set a break at linelineno in the current file.The line number may be prefixed with afilename and a colon,to specify a breakpoint in another file (possibly one that hasn’t been loadedyet). The file is searched onsys.path. Acceptable forms offilenameare/abspath/to/file.py,relpath/file.py,module andpackage.module.

With afunction argument, set a break at the first executable statement withinthat function.function can be any expression that evaluates to a functionin the current namespace.

If a second argument is present, it is an expression which must evaluate totrue before the breakpoint is honored.

Without argument, list all breaks, including for each breakpoint, the numberof times that breakpoint has been hit, the current ignore count, and theassociated condition if any.

Each breakpoint is assigned a number to which all the otherbreakpoint commands refer.

tbreak[([filename:]lineno|function)[,condition]]¶

Temporary breakpoint, which is removed automatically when it is first hit.The arguments are the same as forbreak.

cl(ear)[filename:lineno|bpnumber...]¶

With afilename:lineno argument, clear all the breakpoints at this line.With a space separated list of breakpoint numbers, clear those breakpoints.Without argument, clear all breaks (but first ask confirmation).

disablebpnumber[bpnumber...]¶

Disable the breakpoints given as a space separated list of breakpointnumbers. Disabling a breakpoint means it cannot cause the program to stopexecution, but unlike clearing a breakpoint, it remains in the list ofbreakpoints and can be (re-)enabled.

enablebpnumber[bpnumber...]¶

Enable the breakpoints specified.

ignorebpnumber[count]¶

Set the ignore count for the given breakpoint number. Ifcount is omitted,the ignore count is set to 0. A breakpoint becomes active when the ignorecount is zero. When non-zero, thecount is decremented each time thebreakpoint is reached and the breakpoint is not disabled and any associatedcondition evaluates to true.

conditionbpnumber[condition]¶

Set a newcondition for the breakpoint, an expression which must evaluateto true before the breakpoint is honored. Ifcondition is absent, anyexisting condition is removed; i.e., the breakpoint is made unconditional.

commands[bpnumber]¶

Specify a list of commands for breakpoint numberbpnumber. The commandsthemselves appear on the following lines. Type a line containing justend to terminate the commands. An example:

(Pdb)commands1(com)psome_variable(com)end(Pdb)

To remove all commands from a breakpoint, typecommands and follow itimmediately withend; that is, give no commands.

With nobpnumber argument,commands refers to the last breakpoint set.

You can use breakpoint commands to start your program up again. Simply usethecontinue command, orstep,or any other command that resumes execution.

Specifying any command resuming execution(currentlycontinue,step,next,return,until,jump,quit and their abbreviations)terminates the command list (as ifthat command was immediately followed by end). This is because any time youresume execution (even with a simple next or step), you may encounter anotherbreakpoint—which could have its own command list, leading to ambiguities aboutwhich list to execute.

If the list of commands contains thesilent command, or a command thatresumes execution, then the breakpoint message containing information aboutthe frame is not displayed.

Changed in version 3.14:Frame information will not be displayed if a command that resumes executionis present in the command list.

s(tep)¶

Execute the current line, stop at the first possible occasion (either in afunction that is called or on the next line in the current function).

n(ext)¶

Continue execution until the next line in the current function is reached orit returns. (The difference betweennext andstep isthatstep stops inside a called function, whilenextexecutes called functions at (nearly) full speed, only stopping at the nextline in the current function.)

unt(il)[lineno]¶

Without argument, continue execution until the line with a number greaterthan the current one is reached.

Withlineno, continue execution until a line with a number greater orequal tolineno is reached. In both cases, also stop when the current framereturns.

Changed in version 3.2:Allow giving an explicit line number.

r(eturn)¶

Continue execution until the current function returns.

c(ont(inue))¶

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-mostframe. This lets you jump back and execute code again, or jump forward toskip code that you don’t want to run.

It should be noted that not all jumps are allowed – for instance it is notpossible to jump into the middle of afor loop or out of afinally clause.

l(ist)[first[,last]]¶

List source code for the current file. Without arguments, list 11 linesaround the current line or continue the previous listing. With. asargument, list 11 lines around the current line. 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.

The current line in the current frame is indicated by->. If anexception is being debugged, the line where the exception was originallyraised or propagated is indicated by>>, if it differs from the currentline.

Changed in version 3.2:Added the>> marker.

ll|longlist¶

List all source code for the current function or frame. Interesting linesare marked as forlist.

Added in version 3.2.

a(rgs)¶

Print the arguments of the current function and their current values.

pexpression¶

Evaluateexpression in the current context and print its value.

Note

print() can also be used, but is not a debugger command — this executes thePythonprint() function.

ppexpression¶

Like thep command, except the value ofexpression ispretty-printed using thepprint module.

whatisexpression¶

Print the type ofexpression.

sourceexpression¶

Try to get source code ofexpression and display it.

Added in version 3.2.

display[expression]¶

Display the value ofexpression if it changed, each time execution stopsin the current frame.

Withoutexpression, list all display expressions for the current frame.

Note

Display evaluatesexpression and compares to the result of the previousevaluation ofexpression, so when the result is mutable, display may notbe able to pick up the changes.

Example:

lst=[]breakpoint()passlst.append(1)print(lst)

Display won’t realizelst has been changed because the result of evaluationis modified in place bylst.append(1) before being compared:

>example.py(3)<module>()->pass(Pdb)displaylstdisplaylst:[](Pdb)n>example.py(4)<module>()->lst.append(1)(Pdb)n>example.py(5)<module>()->print(lst)(Pdb)

You can do some tricks with copy mechanism to make it work:

>example.py(3)<module>()->pass(Pdb)displaylst[:]displaylst[:]:[](Pdb)n>example.py(4)<module>()->lst.append(1)(Pdb)n>example.py(5)<module>()->print(lst)displaylst[:]:[1][old:[]](Pdb)

Added in version 3.2.

undisplay[expression]¶

Do not displayexpression anymore in the current frame. Withoutexpression, clear all display expressions for the current frame.

Added in version 3.2.

interact¶

Start an interactive interpreter (using thecode module) in a newglobal namespace initialised from the local and global namespaces for thecurrent scope. Useexit() orquit() to exit the interpreter andreturn to the debugger.

Note

Asinteract creates a new dedicated namespace for code execution,assignments to variables will not affect the original namespaces.However, modifications to any referenced mutable objects will be reflectedin the original namespaces as usual.

Added in version 3.2.

Changed in version 3.13:exit() andquit() can be used to exit theinteractcommand.

Changed in version 3.13:interact directs its output to the debugger’soutput channel rather thansys.stderr.

alias[name[command]]¶

Create an alias calledname that executescommand. Thecommand mustnot be enclosed in quotes. Replaceable parameters can be indicated by%1,%2, … and%9, while%* is replaced by all the parameters.Ifcommand is omitted, the current alias forname is shown. If noarguments are given, all aliases are listed.

Aliases may be nested and can contain anything that can be legally typed atthe pdb prompt. Note that internal pdb commandscan be overridden byaliases. Such a command is then hidden until the alias is removed. Aliasingis recursively applied to the first word of the command line; all other wordsin 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")aliaspiforkin%1.__dict__.keys():print(f"%1.{k} ={%1.__dict__[k]}")# Print instance variables in selfaliaspspiself

unaliasname¶

Delete the specified aliasname.

!statement¶

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 statementresembles a debugger command, e.g.:

(Pdb) ! n=42(Pdb)

To set a global variable, you can prefix the assignment command with aglobal statement on the same line, e.g.:

(Pdb) global list_options; list_options = ['-l'](Pdb)

run[args...]¶

restart[args...]¶

Restart the debugged Python program. Ifargs is supplied, it is splitwithshlex and the result is used as the newsys.argv.History, breakpoints, actions and debugger options are preserved.restart is an alias forrun.

Changed in version 3.14:run andrestart commands are disabled when thedebugger is invoked in'inline' mode.

q(uit)¶

Quit from the debugger. The program being executed is aborted.An end-of-file input is equivalent toquit.

A confirmation prompt will be shown if the debugger is invoked in'inline' mode. Eithery,Y,<Enter> orEOFwill confirm the quit.

Changed in version 3.14:A confirmation prompt will be shown if the debugger is invoked in'inline' mode. After the confirmation, the debugger will callsys.exit() immediately, instead of raisingbdb.BdbQuitin the next trace event.

debugcode¶

Enter a recursive debugger that steps throughcode(which is an arbitrary expression or statement to beexecuted in the current environment).

retval¶

Print the return value for the last return of the current function.

exceptions[excnumber]¶

List or jump between chained exceptions.

When usingpdb.pm() orPdb.post_mortem(...) with a chained exceptioninstead of a traceback, it allows the user to move between thechained exceptions usingexceptions command to list exceptions, andexceptions<number> to switch to that exception.

Example:

defout():try:middle()exceptExceptionase:raiseValueError("reraise middle() error")fromedefmiddle():try:returninner(0)exceptExceptionase:raiseValueError("Middle fail")definner(x):1/xout()

callingpdb.pm() will allow to move between exceptions:

>example.py(5)out()->raiseValueError("reraise middle() error")frome(Pdb)exceptions0ZeroDivisionError('division by zero')1ValueError('Middle fail')>2ValueError('reraise middle() error')(Pdb)exceptions0>example.py(16)inner()->1/x(Pdb)up>example.py(10)middle()->returninner(0)

Added in version 3.13.

Footnotes

Whether a frame is considered to originate in a certain moduleis determined by the__name__ in the frame globals.