code — Interpreter base classes
Source code: Lib/code.py
code module provides facilities to implement read-eval-print loops in Python. Two classes and convenience functions are included which can be used to build applications which provide an interactive interpreter prompt.
This class deals with parsing and interpreter state (the user’s namespace); it does not deal with input buffering or prompting or input file naming (the filename is always passed in explicitly). The optional locals argument specifies the dictionary in which code will be executed; it defaults to a newly created dictionary with key
class code.InteractiveConsole(locals=None, filename="<console>")
Closely emulate the behavior of the interactive Python interpreter. This class builds on
InteractiveInterpreterand adds prompting using the familiar
sys.ps2, and input buffering.
code.interact(banner=None, readfunc=None, local=None, exitmsg=None)
Convenience function to run a read-eval-print loop. This creates a new instance of
InteractiveConsoleand sets readfunc to be used as the
InteractiveConsole.raw_input()method, if provided. If local is provided, it is passed to the
InteractiveConsoleconstructor for use as the default namespace for the interpreter loop. The
interact()method of the instance is then run with banner and exitmsg passed as the banner and exit message to use, if provided. The console object is discarded after use.
Changed in version 3.6: Added exitmsg parameter.
code.compile_command(source, filename="<input>", symbol="single")
This function is useful for programs that want to emulate Python’s interpreter main loop (a.k.a. the read-eval-print loop). The tricky part is to determine when the user has entered an incomplete command that can be completed by entering more text (as opposed to a complete command or a syntax error). This function almost always makes the same decision as the real interpreter main loop.
source is the source string; filename is the optional filename from which source was read, defaulting to
'<input>'; and symbol is the optional grammar start symbol, which should be
Returns a code object (the same as
compile(source, filename, symbol)) if the command is complete and valid;
Noneif the command is incomplete; raises
SyntaxErrorif the command is complete and contains a syntax error, or raises
ValueErrorif the command contains an invalid literal.
Interactive Interpreter Objects
InteractiveInterpreter.runsource(source, filename="<input>", symbol="single")
Compile and run some source in the interpreter. Arguments are the same as for
compile_command(); the default for filename is
'<input>', and for symbol is
'single'. One of several things can happen:
- The input is incorrect;
compile_command()raised an exception (
OverflowError). A syntax traceback will be printed by calling the
- The input is incomplete, and more input is required;
- The input is complete;
compile_command()returned a code object. The code is executed by calling the
runcode()(which also handles run-time exceptions, except for
The return value can be used to decide whether to use
sys.ps2to prompt the next line.
- The input is incorrect;
Execute a code object. When an exception occurs,
showtraceback()is called to display a traceback. All exceptions are caught except
SystemExit, which is allowed to propagate.
A note about
KeyboardInterrupt: this exception may occur elsewhere in this code, and may not always be caught. The caller should be prepared to deal with it.
Display the syntax error that just occurred. This does not display a stack trace because there isn’t one for syntax errors. If filename is given, it is stuffed into the exception instead of the default filename provided by Python’s parser, because it always uses
'<string>'when reading from a string. The output is written by the
Display the exception that just occurred. We remove the first stack item because it is within the interpreter object implementation. The output is written by the
Changed in version 3.5: The full chained traceback is displayed instead of just the primary traceback.
Write a string to the standard error stream (
sys.stderr). Derived classes should override this to provide the appropriate output handling as needed.
Interactive Console Objects
InteractiveConsole class is a subclass of
InteractiveInterpreter, and so offers all the methods of the interpreter objects as well as the following additions.
Closely emulate the interactive Python console. The optional banner argument specify the banner to print before the first interaction; by default it prints a banner similar to the one printed by the standard Python interpreter, followed by the class name of the console object in parentheses (so as not to confuse this with the real interpreter – since it’s so close!).
The optional exitmsg argument specifies an exit message printed when exiting. Pass the empty string to suppress the exit message. If exitmsg is not given or
None, a default message is printed.
Changed in version 3.4: To suppress printing any banner, pass an empty string.
Changed in version 3.6: Print an exit message when exiting.
Push a line of source text to the interpreter. The line should not have a trailing newline; it may have internal newlines. The line is appended to a buffer and the interpreter’s
runsource()method is called with the concatenated contents of the buffer as source. If this indicates that the command was executed or invalid, the buffer is reset; otherwise, the command is incomplete, and the buffer is left as it was after the line was appended. The return value is
Trueif more input is required,
Falseif the line was dealt with in some way (this is the same as
Remove any unhandled source text from the input buffer.
Write a prompt and read a line. The returned line does not include the trailing newline. When the user enters the EOF key sequence,
EOFErroris raised. The base implementation reads from
sys.stdin; a subclass may replace this with a different implementation.
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