io — file-like streams

import io

In-memory streams + the IOBase ABC. open() returns objects that follow this protocol; you can build your own with the same shape.

io.StringIO(initial='') — in-memory text stream

buf = io.StringIO()
buf.write('hello ')
buf.write('world')
buf.getvalue()             # 'hello world'

# Read from one:
buf = io.StringIO('line 1\nline 2\n')
buf.readline()             # 'line 1\n'
buf.read()                 # 'line 2\n'

Useful when an API wants a file-like and you want a string. For example, capturing print() output:

import sys, io
saved = sys.stdout
sys.stdout = io.StringIO()
print('captured!')
captured = sys.stdout.getvalue()
sys.stdout = saved
print('was:', repr(captured))

io.BytesIO(initial=b'') — same, but bytes

buf = io.BytesIO()
buf.write(b'\x00\x01\xff')
buf.getvalue()             # b'\x00\x01\xff'

buf = io.BytesIO(b'hello')
buf.read(3)                # b'hel'
buf.seek(0)                # back to start
buf.read()                 # b'hello'

io.IOBase — base class

Subclass to make your own file-like object. Required methods (any subset you actually use):

• .read(n=-1) / .write(buf) / .close()
• .readinto(buf, n=-1) — read into a pre-allocated buffer
• .seek(offset, whence=0) / .tell()
• .readable(), .writable(), .seekable() — returns bool

Useful for adapting one stream into another (e.g. a TCP socket adapted as a line-oriented text stream).

File objects (returned by open())

In addition to the IOBase methods:

• Iteration yields lines: for line in f: ...
• with works: with open(path) as f: ...
• .flush() is a no-op (DOS write doesn’t buffer)

See DOS file I/O for 8.3 filename / line ending details.

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Credit: shape from MicroPython io docs (MIT).