environment/lib/python2.7/site-packages/IPython/external/pexpect/_pexpect.py
def which (filename):

    """This takes a given filename; tries to find it in the environment path;
    then checks if it is executable. This returns the full path to the filename
    if found and executable. Otherwise this returns None."""

    # Special case where filename already contains a path.
    if os.path.dirname(filename) != '':
        if os.access (filename, os.X_OK):
            return filename

    if not os.environ.has_key('PATH') or os.environ['PATH'] == '':
        p = os.defpath
    else:
        p = os.environ['PATH']

    pathlist = p.split(os.pathsep)

    for path in pathlist:
        f = os.path.join(path, filename)
        if os.access(f, os.X_OK):
            return f
    return None
def which (filename):

    # Special case where filename already contains a path.
    if os.path.dirname(filename) != '':
        if os.access (filename, os.X_OK):
            return filename

    if not os.environ.has_key('PATH') or os.environ['PATH'] == '':
        p = os.defpath
    else:
        p = os.environ['PATH']

    pathlist = p.split(os.pathsep)

    for path in pathlist:
        f = os.path.join(path, filename)
        if os.access(f, os.X_OK):
            return f
    return None
def which ( filename ) : # Special case where filename already contains a path. if os . path . dirname ( filename ) != '' : if os . access ( filename , os . X_OK ) : return filename if not os . environ . has_key ( 'PATH' ) or os . environ [ 'PATH' ] == '' : p = os . defpath else : p = os . environ [ 'PATH' ] pathlist = p . split ( os . pathsep ) for path in pathlist : f = os . path . join ( path , filename ) if os . access ( f , os . X_OK ) : return f return None
This takes a given filename; tries to find it in the environment path;
    then checks if it is executable. This returns the full path to the filename
    if found and executable. Otherwise this returns None.
This takes a given filename ; tries to find it in the environment path ; then checks if it is executable . This returns the full path to the filename if found and executable . Otherwise this returns None .