cpython/Lib/codeop.py at cfc21fcf48d97149541d1a5cc8d4ac2e550780fe · python/cpython · GitHub

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"""Utility to compile possibly incomplete Python source code."""

__all__ = ["compile_command"]

def compile_command(source, filename="<input>", symbol="single"):

r"""Compile a command and determine whether it is incomplete.

Arguments:

source -- the source string; may contain \n characters

filename -- optional filename from which source was read; default "<input>"

symbol -- optional grammar start symbol; "single" (default) or "eval"

Return value / exceptions raised:

- Return a code object if the command is complete and valid

- Return None if the command is incomplete

- Raise SyntaxError or OverflowError if the command is a syntax error

(OverflowError if the error is in a numeric constant)

Approach:

First, check if the source consists entirely of blank lines and

comments; if so, replace it with 'pass', because the built-in

parser doesn't always do the right thing for these.

Compile three times: as is, with \n, and with \n\n appended. If

it compiles as is, it's complete. If it compiles with one \n

appended, we expect more. If it doesn't compile either way, we

compare the error we get when compiling with \n or \n\n appended.

If the errors are the same, the code is broken. But if the errors

are different, we expect more. Not intuitive; not even guaranteed

to hold in future releases; but this matches the compiler's

behavior from Python 1.4 through 1.5.2, at least.

Caveat:

It is possible (but not likely) that the parser stops parsing

with a successful outcome before reaching the end of the source;

in this case, trailing symbols may be ignored instead of causing an

error. For example, a backslash followed by two newlines may be

followed by arbitrary garbage. This will be fixed once the API

for the parser is better.

"""

# Check for source consisting of only blank lines and comments

for line in source.split("\n"):

line = line.strip()

if line and line[0] != '#':

break # Leave it alone

else:

source = "pass" # Replace it with a 'pass' statement

err = err1 = err2 = None

code = code1 = code2 = None

try:

code = compile(source, filename, symbol)

except SyntaxError, err:

pass

try:

code1 = compile(source + "\n", filename, symbol)

except SyntaxError, err1:

pass

try:

code2 = compile(source + "\n\n", filename, symbol)

except SyntaxError, err2:

pass

if code:

return code

try:

e1 = err1.__dict__

except AttributeError:

e1 = err1

try:

e2 = err2.__dict__

except AttributeError:

e2 = err2

if not code1 and e1 == e2:

raise SyntaxError, err1

cpython/Lib/codeop.py at cfc21fcf48d97149541d1a5cc8d4ac2e550780fe · python/cpython · GitHub

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