how to replace a line in a file in python

Question

I want to replace a string in a file created by my program, But I cant use .replace because It's not in 3.3, How do I replace a line from a file using two inputs(the previous string, replacement), Here Is the code so far:

#Data Creator
def Create(filename):
    global UserFile
    UserFile = open(str(filename), "w")
    global file
    file = (filename)
    UserFile.close()

#Data Adder
def Add(data):
    UserFile = open(file, "a")
    UserFile.write(str(data))
    UserFile.close()

#Data seeker
def Seek(target):
    UserFile = open(file, "r")
    UserFile.seek(target)
    global postition
    position = UserFile.tell(target)
    UserFile.close()
    return position

#Replace
def Replace(take,put):
    UserFile = open(file, "r+")
    UserFile.replace(take,put)
    UserFile.close

Create("richardlovesdogs.txt")
Add("Richard loves all kinds of dogs including: \nbeagles")
Replace("beagles","pugs")

How do I do this, So that It replaces the word "beagles" with "pugs"? I'm learning python so any help would be appreciated

Edit :

ive changed the replace code to this

#Replace
def Replace(take,put):
    UserFile = open(file, 'r+')
    UserFileT = open(file, 'r+')
    for line in UserFile:
        UserFileT.write(line.replace(take,put))
    UserFile.close()
    UserFileT.close()

but in the file it outputs:

Richard loves all kinds of dogs including: 
pugsles

how do i change it so it outputs only "pugs" not "pugsles"

str.replace() is a method on strings. It is not a method on a file object. It never was. — Martijn Pieters
– Martijn Pieters, Commented Aug 30, 2013 at 17:42
Im sure I read it somewhere, must be a mistake what other way Is there then? — Jaf
– Jaf, Commented Aug 30, 2013 at 17:43
@Jaffar Start here: docs.python.org/3/tutorial/…; Related: find and replace within a text file — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Aug 30, 2013 at 17:46
possible duplicate of How to search and replace in a file using python — Martijn Pieters
– Martijn Pieters, Commented Aug 30, 2013 at 17:46

mic4ael · Accepted Answer · 2013-08-30 17:44:37Z

0

The first idea which came to my mind is to loop over lines and check if the given line contains the word which you want to replace. Then just use string method - replace. Of course, in the end the result should be put/written to the file.

answered Aug 30, 2013 at 17:44

mic4ael

8,4304 gold badges32 silver badges44 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Jaf Over a year ago

would this mean putting the entire file into a string then editing it? effectively overwriting the whole file?

mic4ael Over a year ago

you can use method readlines which create a list of lines for a given file, then you can loop over the list.

Ashwini Chaudhary Over a year ago

@mic4ael file.readlines also loads the whole file into memory, simply iterate over the file object to load one line at a time.

Steven Rumbalski Over a year ago

Take note that str.replace will replace parts of words: 'man command'.replace('man', 'woman') gives 'woman comwomand' which is probably not what was wanted.

mikeba · Accepted Answer · 2013-08-30 17:50:01Z

0

Perhaps what you were thinking of was the sed command in Unix shell, which will let you replace a specific text in a file with a replacement text from the shell itself.

As others have said, replacing text in Python has always been str.replace().

Hope this helps!

answered Aug 30, 2013 at 17:50

mikeba

242 bronze badges

Comments

blakev · Accepted Answer · 2013-08-30 21:59:56Z

0

The fastest way to do this, without loading the whole file into memory, is using the file seek, tell and flush. Set your starting pointer to position 0, and increment through the file by len(replacement_word). If the few-byte snippet matches then you set a marker where you are within the file.

After you've scanned the file, you rebuild the file using your markers and joining the segments with your replacement string between them.

answered Aug 30, 2013 at 21:59

blakev

4,5392 gold badges39 silver badges56 bronze badges

Collectives™ on Stack Overflow

how to replace a line in a file in python

Edit :

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Edit :

3 Answers 3

4 Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related