Python Read Files

Python Read Files

Once a file is successfully opened using the open() function, you can read its contents. Python provides multiple methods to extract the data exactly how you need it.

Assume we have a file named demofile.txt located in the same folder as Python, containing the following text:

Hello! Welcome to demofile.txt This file is for testing purposes. Good Luck!

1. Read the Whole File

The read() method reads the entire content of the file and returns it as a single string.

f = open("demofile.txt", "r")
print(f.read())

Read Only Parts of the File

By default, the read() method returns the whole text, but you can also specify how many characters you want to return.

# Return only the first 5 characters
f = open("demofile.txt", "r")
print(f.read(5)) 

2. Read Lines

You can return one line at a time by using the readline() method.

f = open("demofile.txt", "r")
print(f.readline()) # Reads the first line
print(f.readline()) # Reads the second line

If you want to read all the lines and store them as a list where each line is an item, use readlines():

f = open("demofile.txt", "r")
lines_list = f.readlines()
print(lines_list[0])

3. Looping Through a File

By looping through the lines of the file, you can read the whole file line by line. This is incredibly memory-efficient for very large files, because it doesn't load the entire file into memory at once.

f = open("demofile.txt", "r")
for x in f:
  print(x)

4. Close Files

It is considered good practice to always close the file when you are done with it. Unclosed files can cause memory leaks and unpredictable behavior in your applications.

f = open("demofile.txt", "r")
print(f.readline())
f.close()

with open("demofile.txt", "r") as f:
    print(f.read())
# The file is now safely closed automatically.