Replace not working python3

Question

I'm trying to loop through a file and replace all instances of several things.. It's working SOME of the time, but it's missing values that it correctly replaced earlier in the file and I have no idea why it won't work every time.

with open("myfile", "rt") as filein:
with open("mynewfile", "wt") as fileout:
    for line in filein:
        fileout.write(line.replace('a', 'b'))
        fileout.write(line.replace('c', 'd'))
        fileout.write(line.replace('e', 'f'))
        fileout.write(line.replace('g', 'h'))
        fileout.write(line.replace('i', 'j'))
        fileout.write(line.replace('k', 'l'))
print("Done")

The replace method does not mutate the string it returns a new one — taoufik A
– taoufik A, Commented Jan 3, 2018 at 0:05

taoufik A · Accepted Answer · 2018-01-03 01:44:17Z

1

The replace method does not mutate the string it returns a new one
try this

with open("myfile", "rt") as filein, open("mynewfile", "wt") as fileout
        for line in filein:
            line = line.replace('a', 'b')
            fileout.write(line)
            line = line.replace('c', 'd')
            fileout.write(line)
            ...

or better

list_replace = [('a', 'b'), ('c', 'd'), ...]
with open("myfile", "rt") as filein, open("mynewfile", "wt") as fileout
        for line in filein:
            for t in list_replace:
                line = line.replace(*t)
            fileout.write(line)

Update based on the comments

list_replace = [('a', 'b'), ('c', 'd'), ...]
with open("myfile", "rt") as filein, open("mynewfile", "wt") as fileout
        for line in filein:
            tmp = line[36:]
            for t in list_replace:
                tmp = tmp.replace(*t)
            fileout.write(line[:36] + tmp)

edited Jan 3, 2018 at 1:44

answered Jan 3, 2018 at 0:12

taoufik A

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11 Comments

taoufik A Over a year ago

I did not get it , could please explain more

Jake Over a year ago

like this, so it's replacing SOME of the values but missing others even if it caught it earlier line1: original line2: original, original line3: original, replaced line4: replaced, replaced line5: replaced

Jake Over a year ago

it looks like it worked!! thank you so much! what did that change do? it looks like all you did was move the 2nd open to the same line as the first, is there a way to make it start looking to replace at a certain point in the line? there is an ID before the part i'm replacing and it looks like the numbers i'm replacing are in some of those ids

taoufik A Over a year ago

Yep, before it writes the line after each replace operation

Jake Over a year ago

It works perfectly, you rock thank you so much for all the help

|

pstatix · Accepted Answer · 2018-01-03 00:18:38Z

0

Cannot replicate your problem in Python 3. The following works just fine:

with open("myfile", "rt") as filein, open("mynewfile", "wt") as fileout:
    for line in filein:
        fileout.write(line.replace('a', 'b'))
        fileout.write(line.replace('c', 'd'))
        fileout.write(line.replace('e', 'f'))
        fileout.write(line.replace('g', 'h'))
        fileout.write(line.replace('i', 'j'))
        fileout.write(line.replace('k', 'l'))
print("Done")

You have to account for the presence of a \n at the end of filein though, so check for it.

answered Jan 3, 2018 at 0:18

pstatix

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Comments

Kevin Woolery · Accepted Answer · 2018-01-03 00:20:57Z

0

You're writing out 6 lines to fileout for every line you read in from filein. Each new line only replaces 1 character, not all of them.

If you're trying to replace everything in the line, try the following. multi_replace takes a list of search strings, and replace strings, then iterates over them to replace them individually on each line.

def multi_replace(line, searchlist, replacelist):
   for i, j in zip(searchlist, replacelist):
     line = line.replace(i, j)
   return line

with open("myfile", "rt") as filein:
  with open("mynewfile", "wt") as fileout:
    for line in filein:
        fileout.write(multi_replace(line, ['a','c','e','g','i','k'],['b','d','f','h','j','l']))
print("Done")

answered Jan 3, 2018 at 0:20

Kevin Woolery

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