https://docs.python.org/3/library/io.html

Overview

The io module provides Python’s main facilities for dealing with various types of I/O. There are three main types of I/O: text I/O, binary I/O and raw I/O. These are generic categories, and various backing stores can be used for each of them. A concrete object belonging to any of these categories is called a file object. Other common terms are stream and file-like object.

Independent of its category, each concrete stream object will also have various capabilities: it can be read-only, write-only, or read-write. It can also allow arbitrary random access (seeking forwards or backwards to any location), or only sequential access (for example in the case of a socket or pipe).

All streams are careful about the type of data you give to them. For example giving a str object to the write() method of a binary stream will raise a TypeError. So will giving a bytes object to the write() method of a text stream.

Changed in version 3.3: Operations that used to raise IOError now raise OSError, since IOError is now an alias of OSError.

Text I/O

Text I/O expects and produces str objects. This means that whenever the backing store is natively made of bytes (such as in the case of a file), encoding and decoding of data is made transparently as well as optional translation of platform-specific newline characters.

The easiest way to create a text stream is with open(), optionally specifying an encoding:

f = open("myfile.txt", "r", encoding="utf-8")

In-memory text streams are also available as StringIO objects:

f = io.StringIO("some initial text data")

The text stream API is described in detail in the documentation of TextIOBase.

Binary I/O

Binary I/O (also called buffered I/O) expects bytes-like objects and produces bytes objects. No encoding, decoding, or newline translation is performed. This category of streams can be used for all kinds of non-text data, and also when manual control over the handling of text data is desired.

The easiest way to create a binary stream is with open() with 'b' in the mode string:

f = open("myfile.jpg", "rb")

In-memory binary streams are also available as BytesIO objects:

f = io.BytesIO(b"some initial binary data: \x00\x01")

The binary stream API is described in detail in the docs of BufferedIOBase.

Other library modules may provide additional ways to create text or binary streams. See socket.socket.makefile() for example.

Raw I/O

Raw I/O (also called unbuffered I/O) is generally used as a low-level building-block for binary and text streams; it is rarely useful to directly manipulate a raw stream from user code. Nevertheless, you can create a raw stream by opening a file in binary mode with buffering disabled:

f = open("myfile.jpg", "rb", buffering=0)

The raw stream API is described in detail in the docs of RawIOBase.