Lib/codeop.py

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