How to replace multiple substrings of a string?

Question

I would like to use the .replace function to replace multiple strings.

I currently have

string.replace("condition1", "")

but would like to have something like

string.replace("condition1", "").replace("condition2", "text")

although that does not feel like good syntax

what is the proper way to do this? kind of like how in grep/regex you can do \1 and \2 to replace fields to certain search strings

Answer 1

You could just make a nice little looping function.

def replace_all(text, dic):
    for i, j in dic.iteritems():
        text = text.replace(i, j)
    return text

where text is the complete string and dic is a dictionary — each definition is a string that will replace a match to the term.

Note: in Python 3, iteritems() has been replaced with items()

---

Careful: Python dictionaries don't have a reliable order for iteration. This solution only solves your problem if:

• order of replacements is irrelevant
• it's ok for a replacement to change the results of previous replacements

For instance:

d = { "cat": "dog", "dog": "pig"}
mySentence = "This is my cat and this is my dog."
replace_all(mySentence, d)
print(mySentence)

Possible output #1:

"This is my pig and this is my pig."

Possible output #2

"This is my dog and this is my pig."

One possible fix is to use an OrderedDict.

from collections import OrderedDict
def replace_all(text, dic):
    for i, j in dic.items():
        text = text.replace(i, j)
    return text
od = OrderedDict([("cat", "dog"), ("dog", "pig")])
mySentence = "This is my cat and this is my dog."
replace_all(mySentence, od)
print(mySentence)

Output:

"This is my pig and this is my pig."

---

Careful #2: Inefficient if your text string is too big or there are many pairs in the dictionary.

Answer 2

Here is a variant of the first solution using reduce, in case you like being functional. :)

repls = {'hello' : 'goodbye', 'world' : 'earth'}
s = 'hello, world'
reduce(lambda a, kv: a.replace(*kv), repls.iteritems(), s)

martineau's even better version:

repls = ('hello', 'goodbye'), ('world', 'earth')
s = 'hello, world'
reduce(lambda a, kv: a.replace(*kv), repls, s)

Answer 3

Or just for a fast hack:

for line in to_read:
    read_buffer = line              
    stripped_buffer1 = read_buffer.replace("term1", " ")
    stripped_buffer2 = stripped_buffer1.replace("term2", " ")
    write_to_file = to_write.write(stripped_buffer2)

Answer 4

this is my solution to the problem. I used it in a chatbot to replace the different words at once.

def mass_replace(text, dct):
    new_string = ""
    old_string = text
    while len(old_string) > 0:
        s = ""
        sk = ""
        for k in dct.keys():
            if old_string.startswith(k):
                s = dct[k]
                sk = k
        if s:
            new_string+=s
            old_string = old_string[len(sk):]
        else:
            new_string+=old_string[0]
            old_string = old_string[1:]
    return new_string

print mass_replace("The dog hunts the cat", {"dog":"cat", "cat":"dog"})

this will become The cat hunts the dog

Answer 5

In my case, I needed a simple replacing of unique keys with names, so I thought this up:

a = 'This is a test string.'
b = {'i': 'I', 's': 'S'}
for x,y in b.items():
    a = a.replace(x, y)
>>> a
'ThIS IS a teSt StrIng.'

Answer 6

Starting from the precious answer of Andrew i developed a script that loads the dictionary from a file and elaborates all the files on the opened folder to do the replacements. The script loads the mappings from an external file in which you can set the separator. I'm a beginner but i found this script very useful when doing multiple substitutions in multiple files. It loaded a dictionary with more than 1000 entries in seconds. It is not elegant but it worked for me

import glob
import re

mapfile = input("Enter map file name with extension eg. codifica.txt: ")
sep = input("Enter map file column separator eg. |: ")
mask = input("Enter search mask with extension eg. 2010*txt for all files to be processed: ")
suff = input("Enter suffix with extension eg. _NEW.txt for newly generated files: ")

rep = {} # creation of empy dictionary

with open(mapfile) as temprep: # loading of definitions in the dictionary using input file, separator is prompted
    for line in temprep:
        (key, val) = line.strip('\n').split(sep)
        rep[key] = val

for filename in glob.iglob(mask): # recursion on all the files with the mask prompted

    with open (filename, "r") as textfile: # load each file in the variable text
        text = textfile.read()

        # start replacement
        #rep = dict((re.escape(k), v) for k, v in rep.items()) commented to enable the use in the mapping of re reserved characters
        pattern = re.compile("|".join(rep.keys()))
        text = pattern.sub(lambda m: rep[m.group(0)], text)

        #write of te output files with the prompted suffice
        target = open(filename[:-4]+"_NEW.txt", "w")
        target.write(text)
        target.close()