1r"""Utilities to compile possibly incomplete Python source code.
2
3This module provides two interfaces, broadly similar to the builtin
4function compile(), which take program text, a filename and a 'mode'
5and:
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
13Approach:
14
15First, check if the source consists entirely of blank lines and
16comments; if so, replace it with 'pass', because the built-in
17parser doesn't always do the right thing for these.
18
19Compile three times: as is, with \n, and with \n\n appended.  If it
20compiles as is, it's complete.  If it compiles with one \n appended,
21we expect more.  If it doesn't compile either way, we compare the
22error we get when compiling with \n or \n\n appended.  If the errors
23are the same, the code is broken.  But if the errors are different, we
24expect more.  Not intuitive; not even guaranteed to hold in future
25releases; but this matches the compiler's behavior from Python 1.4
26through 2.2, at least.
27
28Caveat:
29
30It is possible (but not likely) that the parser stops parsing with a
31successful outcome before reaching the end of the source; in this
32case, trailing symbols may be ignored instead of causing an error.
33For example, a backslash followed by two newlines may be followed by
34arbitrary garbage.  This will be fixed once the API for the parser is
35better.
36
37The two interfaces are:
38
39compile_command(source, filename, symbol):
40
41    Compiles a single command in the manner described above.
42
43CommandCompiler():
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
51The module also provides another class:
52
53Compile():
54
55    Instances of this class act like the built-in function compile,
56    but with 'memory' in the sense described above.
57"""
58
59import __future__
60import warnings
61
62_features = [getattr(__future__, fname)
63             for fname in __future__.all_feature_names]
64
65__all__ = ["compile_command", "Compile", "CommandCompiler"]
66
67PyCF_DONT_IMPLY_DEDENT = 0x200          # Matches pythonrun.h
68
69def _maybe_compile(compiler, source, filename, symbol):
70    # Check for source consisting of only blank lines and comments
71    for line in source.split("\n"):
72        line = line.strip()
73        if line and line[0] != '#':
74            break               # Leave it alone
75    else:
76        if symbol != "eval":
77            source = "pass"     # Replace it with a 'pass' statement
78
79    err = err1 = err2 = None
80    code = code1 = code2 = None
81
82    try:
83        code = compiler(source, filename, symbol)
84    except SyntaxError as err:
85        pass
86
87    # Suppress warnings after the first compile to avoid duplication.
88    with warnings.catch_warnings():
89        warnings.simplefilter("ignore")
90        try:
91            code1 = compiler(source + "\n", filename, symbol)
92        except SyntaxError as e:
93            err1 = e
94
95        try:
96            code2 = compiler(source + "\n\n", filename, symbol)
97        except SyntaxError as e:
98            err2 = e
99
100    try:
101        if code:
102            return code
103        if not code1 and repr(err1) == repr(err2):
104            raise err1
105    finally:
106        err1 = err2 = None
107
108def _compile(source, filename, symbol):
109    return compile(source, filename, symbol, PyCF_DONT_IMPLY_DEDENT)
110
111def 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), "exec"
120              or "eval"
121
122    Return value / exceptions raised:
123
124    - Return a code object if the command is complete and valid
125    - Return None if the command is incomplete
126    - Raise SyntaxError, ValueError or OverflowError if the command is a
127      syntax error (OverflowError and ValueError can be produced by
128      malformed literals).
129    """
130    return _maybe_compile(_compile, source, filename, symbol)
131
132class Compile:
133    """Instances of this class behave much like the built-in compile
134    function, but if one is used to compile text containing a future
135    statement, it "remembers" and compiles all subsequent program texts
136    with the statement in force."""
137    def __init__(self):
138        self.flags = PyCF_DONT_IMPLY_DEDENT
139
140    def __call__(self, source, filename, symbol):
141        codeob = compile(source, filename, symbol, self.flags, 1)
142        for feature in _features:
143            if codeob.co_flags & feature.compiler_flag:
144                self.flags |= feature.compiler_flag
145        return codeob
146
147class CommandCompiler:
148    """Instances of this class have __call__ methods identical in
149    signature to compile_command; the difference is that if the
150    instance compiles program text containing a __future__ statement,
151    the instance 'remembers' and compiles all subsequent program texts
152    with the statement in force."""
153
154    def __init__(self,):
155        self.compiler = Compile()
156
157    def __call__(self, source, filename="<input>", symbol="single"):
158        r"""Compile a command and determine whether it is incomplete.
159
160        Arguments:
161
162        source -- the source string; may contain \n characters
163        filename -- optional filename from which source was read;
164                    default "<input>"
165        symbol -- optional grammar start symbol; "single" (default) or
166                  "eval"
167
168        Return value / exceptions raised:
169
170        - Return a code object if the command is complete and valid
171        - Return None if the command is incomplete
172        - Raise SyntaxError, ValueError or OverflowError if the command is a
173          syntax error (OverflowError and ValueError can be produced by
174          malformed literals).
175        """
176        return _maybe_compile(self.compiler, source, filename, symbol)
177