File Handling in Python: Reading and Writing Files

Onto file handling in Python. Opening files, reading and writing content, working with paths, and handling the errors that come up in real projects.

Opening a file

Use the built-in open() function. Pass the filename and an optional mode:

file = open('example.txt', 'r')

'r' is read mode. Other common modes: 'w' (write), 'a' (append), 'b' (binary).

Reading from a file

Once open in read mode, you have several options:

Read the entire file: read() returns everything as one string.

  content = file.read()
  print(content)

Read line by line: readline() returns one line at a time.

  line = file.readline()
  while line:
      print(line, end='')
      line = file.readline()

Read all lines into a list: readlines() returns a list of strings.

  lines = file.readlines()
  print(lines)

Writing to a file

Open in write ('w') or append ('a') mode:

Write mode: creates or overwrites the file.

  with open('example.txt', 'w') as file:
      file.write("Hello Python!")

Append mode: adds to the end without deleting existing content.

  with open('example.txt', 'a') as file:
      file.write("\nAppend this line.")

Using the with statement

with closes the file automatically when the block finishes, even if an exception is raised. Use it by default:

with open('example.txt', 'r') as file:
    content = file.read()
    print(content)

Binary files

For images, PDFs, and other non-text files, use 'rb' or 'wb':

with open('example.pdf', 'rb') as file:
    content = file.read()

File paths

Paths differ between operating systems. os.path helps you build them portably:

import os

file_path = os.path.join('folder', 'example.txt')
with open(file_path, 'r') as file:
    print(file.read())

Error handling

Files go missing. Wrap file operations in try-except:

try:
    with open('non_existent_file.txt', 'r') as file:
        print(file.read())
except FileNotFoundError:
    print("The file does not exist")

JSON files

The json module reads and writes JSON data:

import json

# Writing JSON
data = {"name": "John", "age": 30, "city": "New York"}
with open('data.json', 'w') as file:
    json.dump(data, file)

# Reading JSON
with open('data.json', 'r') as file:
    data = json.load(file)
    print(data)

Use with for every file operation, handle exceptions, and pick the right mode for the job.