File Operations in Python

File Operations

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When writing programs, we often need to interact with files—for example, writing content to a file or reading content from a file. Python provides several functions to work with files.

Opening a File

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Files can be opened for either reading or writing. In Python, this is done as follows:

# Use "r" for reading, "w" for writing
open("file_path", "r", encoding="utf-8")

Reading a File

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After opening a file, reading is straightforward:

f = open("file_path", "r", encoding="utf-8")
print(f.read())  # Read all content and print
print(f.read())  # Prints an empty string

The read() method keeps track of the current position in the file, so the second read will return an empty string. If the file is too large, avoid reading the entire file at once, as it can lead to memory issues. In such cases, use read(number) to read a specific number of bytes.

Additionally, you can use readline() to read one line at a time, and readlines() to read the entire file into a list where each element is a line.

Writing to a File

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Writing is also simple. Use f.write(content) to write content into the file. However, note that opening a file with "w" will clear its existing content.

f = open("file_path", "w", encoding="utf-8")
f.write("Hello world!")
f.close()
# The file now contains: Hello world!

f = open("file_path", "w", encoding="utf-8")
f.write("HI")
f.close()
# The file now contains only: HI

If you want to append to a file instead of overwriting it, use "a" mode:

f = open("file_path", "a", encoding="utf-8")

If the file does not exist, both "w" and "a" modes will create it, but "r" mode will throw an error.

The r+ Mode

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If you want to both read and write, use "r+" mode. It allows reading and writing without clearing the file, but writing starts at the beginning of the file, potentially overwriting existing content.

• If you write fewer characters than the original content, the remaining original content stays.
• If you write more, it only overwrites part of the file—it does not automatically delete the excess original content.

To write at a specific position after reading, use:

f = open("file_path", "r+", encoding="utf-8")
f.seek(5)  # Move the cursor to the 5th byte
f.write("HAHA")
f.close()

To write at the end, simply read first, then write.

Summary

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Closing a File

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After working with a file, always close it to prevent resource leaks or file corruption. Use f.close(). A safer way is using the with statement:

with open("test.txt", "w") as f:
    f.write("Hello, world!")
# f is automatically closed after this block