Lib/codeop.py

   1 """Utility to compile possibly incomplete Python source code."""
   2
   3 import sys
   4 import traceback
   5
   6 __all__ = ["compile_command"]
   7
   8 def compile_command(source, filename="<input>", symbol="single"):
   9     r"""Compile a command and determine whether it is incomplete.
  10
  11     Arguments:
  12
  13     source -- the source string; may contain \n characters
  14     filename -- optional filename from which source was read; default "<input>"
  15     symbol -- optional grammar start symbol; "single" (default) or "eval"
  16
  17     Return value / exceptions raised:
  18
  19     - Return a code object if the command is complete and valid
  20     - Return None if the command is incomplete
  21     - Raise SyntaxError or OverflowError if the command is a syntax error
  22       (OverflowError if the error is in a numeric constant)
  23
  24     Approach:
  25
  26     First, check if the source consists entirely of blank lines and
  27     comments; if so, replace it with 'pass', because the built-in
  28     parser doesn't always do the right thing for these.
  29
  30     Compile three times: as is, with \n, and with \n\n appended.  If
  31     it compiles as is, it's complete.  If it compiles with one \n
  32     appended, we expect more.  If it doesn't compile either way, we
  33     compare the error we get when compiling with \n or \n\n appended.
  34     If the errors are the same, the code is broken.  But if the errors
  35     are different, we expect more.  Not intuitive; not even guaranteed
  36     to hold in future releases; but this matches the compiler's
  37     behavior from Python 1.4 through 1.5.2, at least.
  38
  39     Caveat:
  40
  41     It is possible (but not likely) that the parser stops parsing
  42     with a successful outcome before reaching the end of the source;
  43     in this case, trailing symbols may be ignored instead of causing an
  44     error.  For example, a backslash followed by two newlines may be
  45     followed by arbitrary garbage.  This will be fixed once the API
  46     for the parser is better.
  47
  48     """
  49
  50     # Check for source consisting of only blank lines and comments
  51     for line in source.split("\n"):
  52         line = line.strip()
  53         if line and line[0] != '#':
  54             break               # Leave it alone
  55     else:
  56         source = "pass"         # Replace it with a 'pass' statement
  57
  58     err = err1 = err2 = None
  59     code = code1 = code2 = None
  60
  61     try:
  62         code = compile(source, filename, symbol)
  63     except SyntaxError, err:
  64         pass
  65
  66     try:
  67         code1 = compile(source + "\n", filename, symbol)
  68     except SyntaxError, err1:
  69         pass
  70
  71     try:
  72         code2 = compile(source + "\n\n", filename, symbol)
  73     except SyntaxError, err2:
  74         pass
  75
  76     if code:
  77         return code
  78     try:
  79         e1 = err1.__dict__
  80     except AttributeError:
  81         e1 = err1
  82     try:
  83         e2 = err2.__dict__
  84     except AttributeError:
  85         e2 = err2
  86     if not code1 and e1 == e2:
  87         raise SyntaxError, err1