python - Manipulating substrings found to replace -

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• python regex replace ascii value 2 answers

i want replacement depend on found. ie. example of i'm after might following

def f(x):     return str(int(x) + 1)  print(re.sub(r"(\d)", f(r"\1"), "123"))  #print 234 

however, doesn't work of course. way of doing intend without having keep track of position/length of found string , replacing on next line? ie. i'm looking way in 1 go.

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note actual example i'm working on isn't simple. i'm making function interprets mathematical calculation string input.

eg. "2 + 4 * 6 / 3"

the idea function replace "4 * 6" 24, "24 / 3" 8, , "2 + 8" 10. search appropriate pairs , follow bidmas using regex.

maybe it's simplistic, build simple evaluator applying regexes first on multiply, on add operators, using replacement function:

import re  s = "4 + 6 * 7"  def replfunc(m):     = int(m.group(1))     b = int(m.group(3))     op = m.group(2)     if op=="*":         return str(a*b)     elif op=="+":         return str(a+b)  op in "*+":     s = re.sub("(\d+)\s*({})\s*(\d+)".format(re.escape(op)),replfunc,s) 

here, regex tries match "number operator number" (with optional spaces in between) , calls replacement function on match.

the replacement function acts accordignly, converting integer, peforming relevant operation, , returning string replaced.

of course, isn't designed process parenthesized expressions , never be, consider third-party evaluators instead, simpleeval (searching in pypi gives dozens of results)