Lib/codeop.py

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