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(), 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 as err:
  84         pass
  85
  86     try:
  87         code1 = compiler(source + "\n", filename, symbol)
  88     except SyntaxError as e:
  89         err1 = e
  90
  91     try:
  92         code2 = compiler(source + "\n\n", filename, symbol)
  93     except SyntaxError as e:
  94         err2 = e
  95
  96     if code:
  97         return code
  98     if not code1 and repr(err1) == repr(err2):
  99         raise 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)