file.write() not permanently writing to file python

Question

I have a text file of names, all of which have three spaces at the end of them, which I would like to remove. When I print these names in python, I get output like the follows:

Adeline Panella Â
Winifred Aceto  
See Weckerly Â
Daniell Hildebrand Â
Betsey Coulter  
#there are about 1000 of these names

To remove the extra spaces, I wrote the following script:

import os
script_directory = os.path.dirname(__file__)
file = open(os.path.join(script_directory, "assets/data/names.txt"), 'r')
potential_names = file.read().splitlines()
potential_names = list(filter(None, potential_names))
for item in potential_names:
    print(item)
    item = item[:-3]
    print(item)
file.close()
file = open(os.path.join(script_directory, "assets/data/names.txt"), 'w')
for item in potential_names:
    file.write("{}\n".format(item))
file.close()

It appears to function as expected, as the output is as follows:

Adeline Panella  
Adeline Panella
Winifred Aceto  
Winifred Aceto
See Weckerly  
See Weckerly
Daniell Hildebrand  
Daniell Hildebrand
Betsey Coulter  
Betsey Coulter

HOWEVER: When I run the script a second time, the output is exactly the same, and when I examine the text file, the three spaces at the end remain there. How can I permanently remove this extra spacing?

Answer 1

for item in potential_names:
    print(item)
    item = item[:-3]
    print(item)

When you change item on that third line above, it does not reflect back to the potential_names collection, it simply changes item . That's why it appears to be modifying the string ⁽¹⁾ .

However, later, when you process the collection:

for item in potential_names:

that's the original contents of the collection you're outputting.

One way to get around this is to simply construct a new list with the final three characters removed from each item:

potential_names = [x[:-3] for x in potential_names]

---

⁽¹⁾ Python is generally considered a pure object-oriented language because everything is an object to which names refer.

That has certain limitations in that the expression item = '12345'; item = item[:-3] item = '12345'; item = item[:-3] doesn't change the value of the underlying '12345' string, it creates a new string and changes the value of the item reference to refer to it.

That aspect of the language was a real eye-opener once I figured out how it works.