How to replace text in a txt file with python?

Question

I'm trying to replace text in a .txt file using a .py script. Here's what i have so far:

docname=raw_input("Enter a document name: ")    
fo=open(docname, 'r+')    
string=fo.read()    
replace=raw_input("Enter what you want to replace: ")    
replacewith=raw_input("Enter what you want to replace it with: ")    
out=string.replace(replace,replacewith)    
fo.write(out);    
fo.close()    
print "Check the document!"    
closeInput = raw_input("Press ENTER to exit")

I have a txt file called "test.txt" (in the same directory as the .py script). When I enter "test.txt", it asks what I want to replace, as expected. When I fill out that, it asks for what I want to replace it with.

I fill out that, and the program closes. No "Check the document!" or anything. And worst of all, it doesn't replace it with the second string.

Please help!

Answer 1

you have 2 possibilities:

1. if you want to open the file just once, you should reset the position of the stream with fo.seek(0)
2. you can close and reopen the file with fo = open(docname, 'w')

The first option has one problem: if the replace-text is shorter than the original-text, some text will be left over at the end. To illustrate what I'm talking of: You have the text '12345' and want to replace '12' with 'a', then the resulting file would contain 'a3455'