File Input & Output

Reading a file:

with open("file.txt", "r") as f:
    content = f.read()       # entire file as string

with open("file.txt", "r") as f:
    lines = f.readlines()    # list of lines

with open("file.txt", "r") as f:
    for line in f:           # line by line (memory efficient)
        print(line.strip())

Writing a file:

with open("output.txt", "w") as f:   # overwrites
    f.write("Hello\n")
    f.write("World\n")

with open("output.txt", "a") as f:   # appends
    f.write("New line\n")

File modes:

"r" — read, "w" — write (overwrite), "a" — append, "rb" — read binary, "wb" — write binary

Always use with: It automatically closes the file even if an error occurs. Never use f = open() without a with block in production code.

Reference:

Wikipedia: I/O

https://en.wikipedia.org/wiki/Input/output