Python 1 Home

File Handling

Key aspects to remember about file handling in Python:

• Opening Files: Use the open() function. Specify the filename and the mode (‘r’ for reading, ‘w’ for writing, ‘a’ for appending, ‘x’ for exclusive creation, ‘b’ for binary, ’t’ for text - ‘r+’ for reading and writing, etc.).

file = open("my_file.txt", "r") #Opens file for reading

• Reading Files:

  • file.read() : Reads the entire file content as a single string.
  • file.readline() : Reads a single line at a time.
  • file.readlines() : Reads all lines into a list of strings.
  • Iteration: You can directly iterate over a file object to read line by line.

file = open("my_file.txt", "r")
contents = file.read() #reads entire file
lines = file.readlines() #reads entire file into list of lines
for line in file: #iterates over lines
  print(line)
file.close() #IMPORTANT: Always close the file!

• Writing to Files:

  • file.write() : Writes a string to the file.
  • Remember to close the file after writing to ensure data is saved.

file = open("my_file.txt", "w")
file.write("This is some text.\n")
file.write("This is another line.\n")
file.close()

• Appending to Files: Use "a" mode to add content to the end of an existing file.

• Error Handling: Use try...except blocks to handle potential FileNotFoundError exceptions.

try:
    file = open("my_file.txt", "r")
    # ... file operations ...
except FileNotFoundError:
    print("File not found!")
finally:
    file.close() #This will still execute even if exception occurs.  Best way to ensure file is closed

• Context Managers (with statement): The preferred way to handle files, automatically closing them even if errors occur.

with open("my_file.txt", "r") as file:
    contents = file.read()
    # ... process contents ...

# File is automatically closed here.

File IO Modes, Handling Binary Files