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'''Contains code for preprocessing text.'''
def preprocess(string, defines):
'''Simple preprocessor function with #ifdef, #else, and #endif support.'''
defines = set(defines)
output = []
stack = [] # stack of booleans: is this block currently active?
lines = string.splitlines(keepends=True)
for line in lines:
stripped_line = line.lstrip()
if stripped_line.startswith("#ifdef"):
define = stripped_line.split()[1]
active = define in defines
stack.append(active)
elif stripped_line.startswith("#else"):
if not stack:
raise SyntaxError("#else without #ifdef")
# flip only the current (top of stack)
stack[-1] = not stack[-1]
elif stripped_line.startswith("#endif"):
if not stack:
raise SyntaxError("#endif without #ifdef")
stack.pop()
else:
# output only if all enclosing blocks are active
if not stack or all(stack):
output.append(line)
if stack:
raise SyntaxError("Unclosed #ifdef")
return ''.join(output)
def strip_double_empty_lines(string):
'''Collapse triple newlines into double newlines.'''
return string.replace('\n\n\n', '\n\n')
def _test():
string = """\
Lorem Ipsum
#ifdef DEBUG
This is debug code.
#ifdef FOO
This is foo code.
#else
This is foo else code.
#endif
#endif
Dolor Sit Amet\
"""
defines = ["DEBUG"]
result = preprocess(string, defines)
print(result)
if __name__ == '__main__':
_test()
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