IPython/core/compilerop.py

"""Compiler tools with improved interactive support.

Provides compilation machinery similar to codeop, but with caching support so
we can provide interactive tracebacks.

Authors
-------
* Robert Kern
* Fernando Perez
* Thomas Kluyver
"""

# Note: though it might be more natural to name this module 'compiler', that
# name is in the stdlib and name collisions with the stdlib tend to produce
# weird problems (often with third-party tools).

#-----------------------------------------------------------------------------
#  Copyright (C) 2010-2011 The IPython Development Team.
#
#  Distributed under the terms of the BSD License.
#
#  The full license is in the file COPYING.txt, distributed with this software.
#-----------------------------------------------------------------------------

#-----------------------------------------------------------------------------
# Imports
#-----------------------------------------------------------------------------

# Stdlib imports
import __future__
from ast import PyCF_ONLY_AST
import codeop
import functools
import hashlib
import linecache
import operator
import time

#-----------------------------------------------------------------------------
# Constants
#-----------------------------------------------------------------------------

# Roughtly equal to PyCF_MASK | PyCF_MASK_OBSOLETE as defined in pythonrun.h,
# this is used as a bitmask to extract future-related code flags.
PyCF_MASK = functools.reduce(operator.or_,
                             (getattr(__future__, fname).compiler_flag
                              for fname in __future__.all_feature_names))

#-----------------------------------------------------------------------------
# Local utilities
#-----------------------------------------------------------------------------

def code_name(code, number=0):
    """ Compute a (probably) unique name for code for caching.
    
    This now expects code to be unicode.
    """
    hash_digest = hashlib.sha1(code.encode("utf-8")).hexdigest()
    # Include the number and 12 characters of the hash in the name.  It's
    # pretty much impossible that in a single session we'll have collisions
    # even with truncated hashes, and the full one makes tracebacks too long
    return '<ipython-input-{0}-{1}>'.format(number, hash_digest[:12])

#-----------------------------------------------------------------------------
# Classes and functions
#-----------------------------------------------------------------------------

class CachingCompiler(codeop.Compile):
    """A compiler that caches code compiled from interactive statements.
    """

    def __init__(self):
        codeop.Compile.__init__(self)
        
        # This is ugly, but it must be done this way to allow multiple
        # simultaneous ipython instances to coexist.  Since Python itself
        # directly accesses the data structures in the linecache module, and
        # the cache therein is global, we must work with that data structure.
        # We must hold a reference to the original checkcache routine and call
        # that in our own check_cache() below, but the special IPython cache
        # must also be shared by all IPython instances.  If we were to hold
        # separate caches (one in each CachingCompiler instance), any call made
        # by Python itself to linecache.checkcache() would obliterate the
        # cached data from the other IPython instances.
        if not hasattr(linecache, '_ipython_cache'):
            linecache._ipython_cache = {}
        if not hasattr(linecache, '_checkcache_ori'):
            linecache._checkcache_ori = linecache.checkcache
        # Now, we must monkeypatch the linecache directly so that parts of the
        # stdlib that call it outside our control go through our codepath
        # (otherwise we'd lose our tracebacks).
        linecache.checkcache = check_linecache_ipython


    def _fix_module_ds(self, module):
        """
        Starting in python 3.7 the AST for mule have changed, and if
        the first expressions encountered is a string it is attached to the 
        `docstring` attribute of the `Module` ast node.

        This breaks IPython, as if this string is the only expression, IPython
        will not return it as the result of the current cell.
        """
        from ast import Str, Expr, Module, fix_missing_locations
        docstring = getattr(module, 'docstring', None)
        if not docstring:
            return module
        new_body=[Expr(Str(docstring, lineno=1, col_offset=0), lineno=1, col_offset=0)]
        new_body.extend(module.body)
        return fix_missing_locations(Module(new_body))
        
    def ast_parse(self, source, filename='<unknown>', symbol='exec'):
        """Parse code to an AST with the current compiler flags active.
        
        Arguments are exactly the same as ast.parse (in the standard library),
        and are passed to the built-in compile function."""
        return self._fix_module_ds(compile(source, filename, symbol, self.flags | PyCF_ONLY_AST, 1))
    
    def reset_compiler_flags(self):
        """Reset compiler flags to default state."""
        # This value is copied from codeop.Compile.__init__, so if that ever
        # changes, it will need to be updated.
        self.flags = codeop.PyCF_DONT_IMPLY_DEDENT

    @property
    def compiler_flags(self):
        """Flags currently active in the compilation process.
        """
        return self.flags
        
    def cache(self, code, number=0):
        """Make a name for a block of code, and cache the code.
        
        Parameters
        ----------
        code : str
          The Python source code to cache.
        number : int
          A number which forms part of the code's name. Used for the execution
          counter.
          
        Returns
        -------
        The name of the cached code (as a string). Pass this as the filename
        argument to compilation, so that tracebacks are correctly hooked up.
        """
        name = code_name(code, number)
        entry = (len(code), time.time(),
                 [line+'\n' for line in code.splitlines()], name)
        linecache.cache[name] = entry
        linecache._ipython_cache[name] = entry
        return name

def check_linecache_ipython(*args):
    """Call linecache.checkcache() safely protecting our cached values.
    """
    # First call the original checkcache as intended
    linecache._checkcache_ori(*args)
    # Then, update back the cache with our data, so that tracebacks related
    # to our compiled codes can be produced.
    linecache.cache.update(linecache._ipython_cache)