Why Work with Files?
Files help us store and retrieve data permanently. Whether you're saving user input, logging errors, or working with data files, file handling is an essential skill!
File Handling Basics
- Opening a file
- Reading or writing data
- Closing the file (VERY IMPORTANT!)
Opening a File
Before we can read or write a file, we need to open it using Python's built-in open() function.
file = open("example.txt", "r") # 'r' means read mode
File Modes
| Mode | Description |
|---|---|
'r' |
Read mode (default) |
'w' |
Write mode (creates a new file or overwrites existing) |
'a' |
Append mode (adds to an existing file) |
'x' |
Exclusive creation (fails if the file exists) |
Reading a File
file = open("example.txt", "r")
content = file.read()
print(content)
file.close() # Always close the file!
Read Line by Line
file = open("example.txt", "r")
for line in file:
print(line.strip()) # Removes extra newlines
file.close()
Writing to a File
file = open("example.txt", "w")
file.write("Hello, Python world!\n")
file.close()
Using 'w' mode will erase the file if it exists!
Appending to a File
file = open("example.txt", "a")
file.write("This is a new line!\n")
file.close()
Best Practice: Using with Statement
The with statement automatically closes the file, so we don’t forget!
with open("example.txt", "r") as file:
content = file.read()
print(content)
# File automatically closed here! Summary
| Action | Method |
|---|---|
| Open a file | open("filename", "mode") |
| Read a file | .read(), .readline(), .readlines() |
| Write to a file | .write("text") (be careful with 'w' mode!) |
| Append to a file | .write("text") in 'a' mode |
| Close a file | .close() (or use with) |
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