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# Extracts initial substring delimited by characters start and end.
# Returns substring, excluding delimiters, and remainder. Example:
# (extracted, remainder) = extract_bracketed( "(n*(n+1)) other", '(', ')' )
# extracted = "n*(n+1)"
# remainder = " other"
# see https://stackoverflow.com/questions/1651487/python-parsing-bracketed-blocks
def extract_bracketed( txt, start, end ):
if (txt[0] != start):
return (None, txt)
cnt = 0
for i in range( 0, len( txt )):
if (txt[i] == start):
cnt += 1
elif (txt[i] == end):
cnt -= 1
if (cnt == 0):
return (txt[1:i], txt[i+1:])
# unbalanced
return (None, txt)
# end
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