Large text file: Fails to convert one character into another in python

Question

I'm pretty new to Python and want to convert one character into another character in a large string .txt file.

I tried running the following code on shell:

#Takes text in letter and converts it
old_text = open("letter.txt", "r")

#Convert old_text to new_text replacing all instances of "a" or into "u"
new_text = old_text.upper().replace("a", "u")
print new_text

However, it returns the error "NameError: name 'old_text' is not defined"

Is there anything else I should do to fix this or am I missing something big here?

Answer 1

First off, open() returns a file handle; you need to read the file from the handle if you want a string.

Then you're upper casing the whole string and searching for a lower case letter, which will never replace anything.

Unless there's part of your code that isn't here, it's unclear to me what's resulting in that error.