6.3 File Reading Methods

We explore the read(), readline(), and readlines() methods for reading content from files, as well as the efficient way to iterate over a file object.

Python offers several methods for reading data from a file opened in read mode. The choice of the appropriate method depends on the file size and how you want to process the data.

`read(size)`: Reads and returns the file content as a single string. Optionally, you can provide a `size` argument to read a specific number of bytes. Caution: Using `read()` without an argument on very large files can consume all of your system's RAM.
`readline()`: Reads a single line from the file, from the current position to the next newline character (`\n`). It is useful when you want to process a file line-by-line manually.
`readlines()`: Reads all lines of the file and returns them as a list of strings. Each list item corresponds to a line in the file and includes the newline character (`\n`). Like `read()`, it can be problematic for very large files.

Tip!

The recommended way to read: `for line in file_object`. This is the most efficient and "Pythonic" way to read a file line-by-line. It does not load the entire file into memory at once, making it ideal for processing large files.

# Create a file for the examples
with open("reading_example.txt", "w", encoding="utf-8") as f:
    f.write("Line 1\n")
    f.write("Line 2\n")
    f.write("Line 3\n")

# 1. read()
with open("reading_example.txt", "r", encoding="utf-8") as f:
    print("With read():\n" + f.read())

# 2. readlines()
with open("reading_example.txt", "r", encoding="utf-8") as f:
    lines_list = f.readlines()
    print("With readlines():\n", lines_list)

# 3. Iteration (loop)
with open("reading_example.txt", "r", encoding="utf-8") as f:
    print("With iteration:")
    for i, line in enumerate(f):
        print(f"  Line {i+1}: {line.strip()}")

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