Python正则表达式替换csv中的字符串

Question

I have a csv file formatted as below:

   cat, mammal[1]
   shark, fish[2]
   dog, mammal[3]
   tiger, mammal[4]
   salmon, fish[5]

I would like to replace all the rows containing mammal along with the square brackets.

The output should be as follows:

cat, mam
shark, fish[2]
dog, mam
tiger, mam
salmon, fish[5]

so far I have a code to read/write the csv file:

import csv


with open('animals.csv', 'r') as fin, open("out.csv",'w') as fout:
        writer = csv.writer(fout)
        for row in csv.reader(fin):
            re.sub(???) #stuck at writing the regular expression
            writer.writerow(row)

Answer 1

You can use the following regex for your replacement:

for row in csv.reader(fin):
    row[1] = re.sub(r'(\s*mam)mal\[\d+\]', '\1', row[1])
    writer.writerow(row)

See demonstration .

Answer 2

No need for regex here:

for row in csv.reader(fin):
    if row[1].startswith("mammal["):
       row[1] = "mam"

Performance wise it's best because

• no regex
• string replacement only if matches, left unchanged otherwise

or even faster with a generator comprehension and writerows :

with open('animals.csv', 'r') as fin, open("out.csv",'w') as fout:
    csv.writer(fout).writerows([row[0],"mam"] if row[1].starswith("mammal[") else row for row in csv.reader(fin))

note: seems that there's a leading space in the second column. In which case, add a space in front of search/replace strings.