Lib/codeop.py

   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(), that take progam text, a filename and a 'mode'
   5 and:
   6
   7 - Return a 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         source = "pass"         # Replace it with a 'pass' statement
  76
  77     err = err1 = err2 = None
  78     code = code1 = code2 = None
  79
  80     try:
  81         code = compiler(source, filename, symbol)
  82     except SyntaxError, err:
  83         pass
  84
  85     try:
  86         code1 = compiler(source + "\n", filename, symbol)
  87     except SyntaxError, err1:
  88         pass
  89
  90     try:
  91         code2 = compiler(source + "\n\n", filename, symbol)
  92     except SyntaxError, err2:
  93         pass
  94
  95     if code:
  96         return code
  97     try:
  98         e1 = err1.__dict__
  99     except AttributeError:
 100         e1 = err1
 101     try:
 102         e2 = err2.__dict__
 103     except AttributeError:
 104         e2 = err2
 105     if not code1 and e1 == e2:
 106         raise SyntaxError, err1
 107
 108 def _compile(source, filename, symbol):
 109     return compile(source, filename, symbol, PyCF_DONT_IMPLY_DEDENT)
 110
 111 def compile_command(source, filename="<input>", symbol="single"):
 112     r"""Compile a command and determine whether it is incomplete.
 113
 114     Arguments:
 115
 116     source -- the source string; may contain \n characters
 117     filename -- optional filename from which source was read; default
 118                 "<input>"
 119     symbol -- optional grammar start symbol; "single" (default) or "eval"
 120
 121     Return value / exceptions raised:
 122
 123     - Return a code object if the command is complete and valid
 124     - Return None if the command is incomplete
 125     - Raise SyntaxError, ValueError or OverflowError if the command is a
 126       syntax error (OverflowError and ValueError can be produced by
 127       malformed literals).
 128     """
 129     return _maybe_compile(_compile, source, filename, symbol)
 130
 131 class Compile:
 132     """Instances of this class behave much like the built-in compile
 133     function, but if one is used to compile text containing a future
 134     statement, it "remembers" and compiles all subsequent program texts
 135     with the statement in force."""
 136     def __init__(self):
 137         self.flags = PyCF_DONT_IMPLY_DEDENT
 138
 139     def __call__(self, source, filename, symbol):
 140         codeob = compile(source, filename, symbol, self.flags, 1)
 141         for feature in _features:
 142             if codeob.co_flags & feature.compiler_flag:
 143                 self.flags |= feature.compiler_flag
 144         return codeob
 145
 146 class CommandCompiler:
 147     """Instances of this class have __call__ methods identical in
 148     signature to compile_command; the difference is that if the
 149     instance compiles program text containing a __future__ statement,
 150     the instance 'remembers' and compiles all subsequent program texts
 151     with the statement in force."""
 152
 153     def __init__(self,):
 154         self.compiler = Compile()
 155
 156     def __call__(self, source, filename="<input>", symbol="single"):
 157         r"""Compile a command and determine whether it is incomplete.
 158
 159         Arguments:
 160
 161         source -- the source string; may contain \n characters
 162         filename -- optional filename from which source was read;
 163                     default "<input>"
 164         symbol -- optional grammar start symbol; "single" (default) or
 165                   "eval"
 166
 167         Return value / exceptions raised:
 168
 169         - Return a code object if the command is complete and valid
 170         - Return None if the command is incomplete
 171         - Raise SyntaxError, ValueError or OverflowError if the command is a
 172           syntax error (OverflowError and ValueError can be produced by
 173           malformed literals).
 174         """
 175         return _maybe_compile(self.compiler, source, filename, symbol)