Read the first line of a file in Python.

Here are several ways to read the first line of a file in Python:

Method 1: Use `readline()`

with open('filename.txt', 'r') as file:
    first_line = file.readline()
    print(first_line)

Note: This method reads the first line of a file until it encounters the '\n' character.

Method 2: Use a for loop

with open('filename.txt', 'r') as file:
    for line in file:
        first_line = line
        break # 退出循环，只获取第一行
    print(first_line)

Method 3: Use `next()`

with open('filename.txt', 'r') as file:
    first_line = next(file)
    print(first_line)

The core of these methods is to open a file and then extract the content of its first line. It is recommended to use the `with` statement to open the file; this statement automatically closes the file after reading its contents, preventing accidental resource leaks.