How can I replace certain string in a string in Python?

Question

I am trying to write two procedures to replace matched strings in a string in python. And I have to write two procedures.

def matched_case(old new): .........

note: inputs are two strings, it returns a replacement converter.

def replacement(x,another_string): ..........

note:inputs are a converter from previous procedure, and a string. It returns the result of applying the converter to the input string.

for example:

a = matched_case('mm','m')
print replacement(a, 'mmmm')
it should return m

another example:

R = matched_case('hih','i')
print replacement(R, 'hhhhhhihhhhh')
it should return hi

I am not sure how can I use loop to do the whole thing. Thanks so much for anyone can give a hint.

Your question is not so clear...can you clean up a bit

Vivek S
– Vivek S

2012-06-01 06:23:59 +00:00
Commented Jun 1, 2012 at 6:23 — Vivek S
– Vivek S, Commented Jun 1, 2012 at 6:23

shihongzhi · Accepted Answer · 2012-06-01 06:50:01Z

3

def subrec(pattern, repl, string):
    while pattern in string:
        string = string.replace(pattern, repl)
    return string

foo('mm', 'm', 'mmmm') return m

foo('hih', 'i', 'hhhhhhihhhhh') return hi

edited Jun 1, 2012 at 6:50

answered Jun 1, 2012 at 6:25

shihongzhi

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3 Comments

jfs Over a year ago

to mimic familiar re.sub signature and to point out that the substitution is recursive: def subrec(pattern, repl, string): ...

pepr Over a year ago

Thinking more about the loop, it can be simplified as while src in a: a = a.replace(src, dst) (no if, no break).

UltraInstinct Over a year ago

@shihongzhi OP wants that in two functions. IMO it is best to use a lambda like I have done below.

UltraInstinct · Accepted Answer · 2012-06-01 06:38:29Z

0

Something on the lines of the below might help:

def matched_case(x,y):
    return x, lambda param: param.replace(x,y)

def replacement(matcher, s):
    while matcher[0] in s:
        s = matcher[1](s)
    return s

print replacement(matched_case('hih','i'), 'hhhhhhihhhhh')
print replacement(matched_case('mm','m'), 'mmmm')

OUTPUT:

hi
m

matched_case(..) returns a replacement-converter, so it is best represented using a lambda (anonymous function to put it simply). This anonymous function wraps up the string to the found and the code that actually replaces it.

answered Jun 1, 2012 at 6:38

UltraInstinct

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