Python: Read/Write to File

By Xah Lee. Date: . Last updated: .

To open a file and write to file do:

f=open('xfile.txt','w')

This creates a file “object”.

The second argument of “open” can be 'w' for write (overwrite exsiting file), 'a' for append, 'r' for read only.

To actually print to or read from file, use the file object's methods.

Read entire file:

text = f.read()

Read one line at a time:

line = f.readline()

Read entire file as a list of lines:

mylist = f.readlines()

To write to file, do:

f.write('yay, first line!\n')

When you are done, close the file:

f.close()

Closing files saves memory while the program is still running. You should always do that.

Here is a complete example of reading in a file and writing it to another file.

# -*- coding: utf-8 -*-
# python

f1 = open("/Users/john/in.txt","r")
f2 = open("/Users/john/out.txt","w")

for xx in f1:
    f2.write(xx)

f1.close()
f2.close()

Using 「with」 to Open File

Alternatively, you can use with:

# -*- coding: utf-8 -*-
# python

# example of opening file, using 「with」

with open("/home/joe/my_file.html", "r") as f:
    for x in f:
        print x

When using with, you do not need to close the file. Python will close any file opened within it, when the with block is done.

thank to Kurt Schwehr for showing me “with”.

If you have a question, put $5 at patreon and message me.

Python by Example

  1. Python Basics
  2. Print Version String
  3. Builtin Help
  4. Quote String
  5. String Operations
  6. String Methods
  7. Format String
  8. True, False
  9. if then else
  10. for, while, Loops
  11. List Basics
  12. Loop Thru List
  13. Map Function to List
  14. List Comprehension
  15. List Methods
  16. Dictionary
  17. Loop Thru Dict
  18. Dict Methods
  19. Function
  20. Class
  21. List Modules
  22. Write a Module
  23. Unicode 🐍

Regex

  1. Regex Basics
  2. Regex Reference

Text Processing

  1. Read/Write File
  2. Traverse Directory
  3. Manipulate Path
  4. Process Unicode
  5. Convert File Encoding
  6. Find Replace in dir
  7. Find Replace by Regex
  8. Count Word Frequency

Web

  1. Send Email
  2. GET Web Page
  3. Web Crawler
  4. HTTP POST
  5. Check Page Load Size
  6. Thumbnail Generation

Misc

  1. JSON
  2. Find Script Path
  3. Get Env Var
  4. System Call
  5. Decompress Gzip
  6. Complex Numbers

Advanced

  1. Sort
  2. Copy Nested List
  3. Tuple vs List
  4. Sets, Union, Intersection
  5. Closure in Python 2
  6. Decorator
  7. Append String in Loop
  8. Timing f timeit
  9. Keyword Arg Default Value Unstable