String replacements using re.sub in python

Question

While learning Python regex, I want to replace all Python 2x like print functions to Python 3x like using re.sub :

import re

with open("py2.py", "r") as f:
    matter = f.read()
mtr = re.sub(r"print\s+\"(.+)\"+",r"print(", matter)
with open("pr.py", "w") as f:
    final = f.write(mtr)

Matter of py2.py is:

print "Anything goes here"
print "Anything" 
print "Something goes here" 

But this code replace print "Anything goes here" to print( , How to capture whole string and replace last quote to ")" a well?

Answer 1

You want to use references to the matching groups in your sostitution:

re.sub(r'print\s+"(.*)"', r'print("\1")', matter)

Used as:

>>> import re
>>> matter = """
... print "Anything goes here"
... print "Anything"
... print "Something goes here"
... """
>>> print(re.sub(r'print\s+"(.*)"', r'print("\1")', matter))

print("Anything goes here")
print("Anything")
print("Something goes here")

---

Note that if your goal is to modify python2 code to be python3 compatible there already exist the 2to3 utility which comes included with python itself.

Answer 2

Try this:

print\s+\"(.+)\"

and replace by this:

 print("\1")

Explanation

You can try this:

import re

regex = r"print\s+\"(.+)\""

test_str = ("print \"Anything goes here\"\n"
    "print \"Anything\" \n"
    "print \"Something goes here\" ")

subst = " print(\"\\1\")"

# You can manually specify the number of replacements by changing the 4th argument
result = re.sub(regex, subst, test_str, 0, re.MULTILINE)

if result:
    print (result)