Walkthrough: Write Then Read

例题: 写入再读取

≈ 8 min · python-file-io · Open in WolfCode

Three tiny functions — write a file, read it back as a string, read it as a list of lines. The `with` statement guarantees the file gets closed.

The three functions

Python · runnable

def write_file(path, content):
    with open(path, "w") as f:
        f.write(content)

def read_file(path):
    with open(path, "r") as f:
        return f.read()

def read_lines(path):
    with open(path, "r") as f:
        return [line.rstrip("\n") for line in f]

# Roundtrip
write_file("demo.txt", "Hello, world!\nLine two.\nLine three.\n")
print("--- read_file ---")
print(read_file("demo.txt"))
print("--- read_lines ---")
for i, line in enumerate(read_lines("demo.txt"), 1):
    print(f"{i}: {line!r}")

Loading Python runtime (~5 MB, one-time)…

Three modes

Mode	Effect on existing file	Use case
`"r"`	(default) read-only, opens at start	Read existing data
`"w"`	erases then writes	Overwrite outputs
`"a"`	appends to the end	Logs, audit trails