1 r"""Utilities to compile possibly incomplete Python source code.

     2 

     3 This module provides two interfaces, broadly similar to the builtin

     4 function compile(), which take program text, a filename and a 'mode'

     5 and:

     6 

     7 - Return code object if the command is complete and valid

     8 - Return None if the command is incomplete

     9 - Raise SyntaxError, ValueError or OverflowError if the command is a

    10   syntax error (OverflowError and ValueError can be produced by

    11   malformed literals).

    12 

    13 Approach:

    14 

    15 First, check if the source consists entirely of blank lines and

    16 comments; if so, replace it with 'pass', because the built-in

    17 parser doesn't always do the right thing for these.

    18 

    19 Compile three times: as is, with \n, and with \n\n appended.  If it

    20 compiles as is, it's complete.  If it compiles with one \n appended,

    21 we expect more.  If it doesn't compile either way, we compare the

    22 error we get when compiling with \n or \n\n appended.  If the errors

    23 are the same, the code is broken.  But if the errors are different, we

    24 expect more.  Not intuitive; not even guaranteed to hold in future

    25 releases; but this matches the compiler's behavior from Python 1.4

    26 through 2.2, at least.

    27 

    28 Caveat:

    29 

    30 It is possible (but not likely) that the parser stops parsing with a

    31 successful outcome before reaching the end of the source; in this

    32 case, trailing symbols may be ignored instead of causing an error.

    33 For example, a backslash followed by two newlines may be followed by

    34 arbitrary garbage.  This will be fixed once the API for the parser is

    35 better.

    36 

    37 The two interfaces are:

    38 

    39 compile_command(source, filename, symbol):

    40 

    41     Compiles a single command in the manner described above.

    42 

    43 CommandCompiler():

    44 

    45     Instances of this class have __call__ methods identical in

    46     signature to compile_command; the difference is that if the

    47     instance compiles program text containing a __future__ statement,

    48     the instance 'remembers' and compiles all subsequent program texts

    49     with the statement in force.

    50 

    51 The module also provides another class:

    52 

    53 Compile():

    54 

    55     Instances of this class act like the built-in function compile,

    56     but with 'memory' in the sense described above.

    57 """

    58 

    59 import __future__

    60 

    61 _features = [getattr(__future__, fname)

    62              for fname in __future__.all_feature_names]

    63 

    64 __all__ = ["compile_command", "Compile", "CommandCompiler"]

    65 

    66 PyCF_DONT_IMPLY_DEDENT = 0x200          # Matches pythonrun.h

    67 

    68 def _maybe_compile(compiler, source, filename, symbol):

    69     # Check for source consisting of only blank lines and comments

    70     for line in source.split("\n"):

    71         line = line.strip()

    72         if line and line[0] != '#':

    73             break               # Leave it alone

    74     else:

    75         if symbol != "eval":

    76             source = "pass"     # Replace it with a 'pass' statement

    77 

    78     err = err1 = err2 = None

    79     code = code1 = code2 = None

    80 

    81     try:

    82         code = compiler(source, filename, symbol)

    83     except SyntaxError, err:

    84         pass

    85 

    86     try:

    87         code1 = compiler(source + "\n", filename, symbol)

    88     except SyntaxError, err1:

    89         pass

    90 

    91     try:

    92         code2 = compiler(source + "\n\n", filename, symbol)

    93     except SyntaxError, err2:

    94         pass

    95 

    96     if code:

    97         return code

    98     if not code1 and repr(err1) == repr(err2):

    99         raise SyntaxError, err1

   100 

   101 def _compile(source, filename, symbol):

   102     return compile(source, filename, symbol, PyCF_DONT_IMPLY_DEDENT)

   103 

   104 def compile_command(source, filename="<input>", symbol="single"):

   105     r"""Compile a command and determine whether it is incomplete.

   106 

   107     Arguments:

   108 

   109     source -- the source string; may contain \n characters

   110     filename -- optional filename from which source was read; default

   111                 "<input>"

   112     symbol -- optional grammar start symbol; "single" (default) or "eval"

   113 

   114     Return value / exceptions raised:

   115 

   116     - Return a code object if the command is complete and valid

   117     - Return None if the command is incomplete

   118     - Raise SyntaxError, ValueError or OverflowError if the command is a

   119       syntax error (OverflowError and ValueError can be produced by

   120       malformed literals).

   121     """

   122     return _maybe_compile(_compile, source, filename, symbol)

   123 

   124 class Compile:

   125     """Instances of this class behave much like the built-in compile

   126     function, but if one is used to compile text containing a future

   127     statement, it "remembers" and compiles all subsequent program texts

   128     with the statement in force."""

   129     def __init__(self):

   130         self.flags = PyCF_DONT_IMPLY_DEDENT

   131 

   132     def __call__(self, source, filename, symbol):

   133         codeob = compile(source, filename, symbol, self.flags, 1)

   134         for feature in _features:

   135             if codeob.co_flags & feature.compiler_flag:

   136                 self.flags |= feature.compiler_flag

   137         return codeob

   138 

   139 class CommandCompiler:

   140     """Instances of this class have __call__ methods identical in

   141     signature to compile_command; the difference is that if the

   142     instance compiles program text containing a __future__ statement,

   143     the instance 'remembers' and compiles all subsequent program texts

   144     with the statement in force."""

   145 

   146     def __init__(self,):

   147         self.compiler = Compile()

   148 

   149     def __call__(self, source, filename="<input>", symbol="single"):

   150         r"""Compile a command and determine whether it is incomplete.

   151 

   152         Arguments:

   153 

   154         source -- the source string; may contain \n characters

   155         filename -- optional filename from which source was read;

   156                     default "<input>"

   157         symbol -- optional grammar start symbol; "single" (default) or

   158                   "eval"

   159 

   160         Return value / exceptions raised:

   161 

   162         - Return a code object if the command is complete and valid

   163         - Return None if the command is incomplete

   164         - Raise SyntaxError, ValueError or OverflowError if the command is a

   165           syntax error (OverflowError and ValueError can be produced by

   166           malformed literals).

   167         """

   168         return _maybe_compile(self.compiler, source, filename, symbol)