How can I tell python to edit another python file?

Question

Right now, I have file.py and it prints the word "Hello" into text.txt.

f = open("text.txt") f.write("Hello") f.close()

I want to do the same thing, but I want to print the word "Hello" into a Python file. Say I wanted to do something like this:

f = open("list.py") f.write("a = 1") f.close

When I opened the file list.py, would it have a variable a with a value 1? How would I go about doing this?

When you open it, it will have the text `a = 1` in it (assuming you open it in write mode). — BrenBarn, Dec 27 '14 at 06:00
Don't forget to add the newline at the end. `write("a=1\n")`. — Keith, Dec 27 '14 at 16:05

Greg · Accepted Answer · 2022-07-18T21:09:34.053

5

If you want to append a new line to the end of a file

with open("file.py", "a") as f:
    f.write("\na = 1")

If you want to write a line to the beginning of a file try creating a new one

with open("file.py") as f:
    lines = f.readlines()

with open("file.py", "w") as f:
    lines.insert(0, "a = 1")
    f.write("\n".join(lines))

edited Jul 18 '22 at 21:09

answered Dec 27 '14 at 06:06

Greg

GLHF · Answer 2 · 2014-12-27T06:12:48.247

1

with open("list.py","a") as f:
    f.write("a=1")

This is simple as you see. You have to open that file in write and read mode (a). Also with open() method is safier and more clear.

Example:

with open("list.py","a") as f:
    f.write("a=1")
    f.write("\nprint(a+1)")

list.py

a=1
print(a+1)

Output from list.py:

>>> 
2
>>>

As you see, there is a variable in list.py called a equal to 1.

edited Dec 27 '14 at 06:12

answered Dec 27 '14 at 06:01

GLHF

score 1 · Answer 3 · answered Dec 27 '14 at 15:47

I would recommend you specify opening mode, when you are opening a file for reading, writing, etc. For example:

for reading:

with open('afile.txt', 'r') as f: # 'r' is a reading mode
    text = f.read()

for writing:

with open('afile.txt', 'w') as f: # 'w' is a writing mode
    f.write("Some text")

If you are opening a file with 'w' (writing) mode, old file content will be removed. To avoid that appending mode exists:

with open('afile.txt', 'a') as f: # 'a' as an appending mode
    f.write("additional text")

For more information, please, read documentation.

3 Answers3