replace strings with placeholders in python

Question

I am trying to replace the variables with placeholders like XXX. The words "hello" and "morning" are printed as-is because they appear in another list. The following code works, but prints extra placeholders.

import re

mylist = ['hello', 'morning']
nm = [
    "Hello World Robot Morning.",
    "Hello Aniket Fine Morning.",
    "Hello Paresh Good and bad Morning.",
]



def punctuations(string):
    pattern = re.compile(r"(?u)\b\w\w+\b")
    result = pattern.match(string)
    myword = result.group()
    return myword


for x in nm:
    newlist = list()
    for y in x.split():
        for z in mylist:
            if z.lower() == punctuations(y.lower()):
                newlist.append(y)
            else:
                newlist.append("xxx")
    print(newlist)

Output:

['Hello', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'Morning.']
['Hello', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'Morning.']
['Hello', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'xxx', 'Morning.']

Expected output:

['Hello', 'xxx', 'xxx',  'Morning.']
['Hello', 'xxx', 'xxx',   'Morning.']
['Hello', 'xxx', 'xxx', 'xxx', 'xxx', 'Morning.']

Can you explain your code, is it a arbitrary exercise, or any specific purpose? — hc_dev
– hc_dev, Commented Dec 1, 2019 at 10:11

hc_dev · Accepted Answer · 2019-12-01 11:00:16Z

3

You're reaching for python's vanilla string functions and regular expressions when actually your problem is better solved with formal parsing using Parsing Expression Grammar (PEP):

For example:

import pyparsing as pp

expr = pp.OneOrMore(pp.Word("hello") | pp.Word("world") | pp.Word(pp.alphas).setParseAction(pp.replaceWith("XXX")))

expr.parseString("hello foo bar world")

Yields:

(['hello', 'XXX', 'XXX', 'world'], {})

See module pyParsing and docs.

edited Dec 1, 2019 at 11:00

hc_dev

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answered Dec 1, 2019 at 9:50

JosefAssad

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1 Comment

hc_dev Over a year ago

Nice, you captured essential behaviour of the OPs code and found an effective library (and concept PEG) to solve it elegantly👍

rivamarco · Accepted Answer · 2019-12-02 10:38:09Z

2

You have to break when you have found the word and only after checking all the elements in my_list evaluate if you have found something, and if not, append the placeholder

for x in nm:
    newlist = list()
    for y in x.split():
        for z in mylist:
            if z.lower() == punctuations(y.lower()):
                newlist.append(y)
                break
        else:
            newlist.append('xxx')
    print(newlist)

edited Dec 2, 2019 at 10:38

user9363390

answered Dec 1, 2019 at 9:47

rivamarco

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