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expect-like tools over a Python stream

Project description


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streamexpect is a library providing cross-platform “expect-like” functionality for generic Python streams and sockets . It is similar to the Pexpect library, except where Pexpect explicitly requires an underlying file (usually a TTY), streamexpect uses duck-typing and requires only a read or recv method.

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The original version of streamexpect was generously donated by Digi Wireless Design Services. The software is provided as Alpha software and has not undergone formal testing. It does, however, ship with extensive unit testing.

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Installation is performed using pip. The latest released version of streamexpect can be obtained with the following command:

$ pip install streamexpect

To install the development version from GitHub:

$ pip install -U -e 'git+'


The following example shows opening a serial port (on a Windows PC), sending the uname command, and verifying that Linux is in the returned data.

import serial
import streamexpect

# timeout=0 is essential, as streams are required to be non-blocking
ser = serial.Serial('COM1', baudrate=115200, timeout=0)

with streamexpect.wrap(ser) as stream:
  stream.write('\r\nuname -a\r\n')
  match = stream.expect_bytes('Linux', timeout=1.0)
  print(u'Found Linux at index {}'.format(match.start))

Design Goals

  • Be Cross-Platform

The library should not depend on any features (besides Python) that exclude a platform. Yes, that means Windows is a first-class citizen.

  • Be Explicit In Encoding

When dealing with streams of data, the distinction between when the stream goes from being a series of binary bytes to a set of encoded characters can be unclear. The library should be explicit in the handling of binary versus characters, such that mixing the two types is not allowed without explicit options to enable encoding and decoding.

  • Common Use Cases Should Be Simple

For 95% of users, the streamexpect.wrap function should accomplish the desired goals. Intelligent default options should be used so the library just “does the right thing”.

  • Complicated Use Cases Should Be Possible

The objects returned by the streamexpect.wrap function should themselves be easy to use and extend. Protocol requirements between classes should be explicit and documented.


Development of streamexpect takes place in the open on GitHub. Please use pull requests to submit changes to code and documentation.

The process for building and testing streamexpect has been automated as much as possible. tox handles building and testing the code, as well as generating documentation and automatically testing for code style issues. tox can be installed with pip:

pip install tox

The generic tox command looks like:


This will attempt to build and test streamexpect against multiple different versions of Python, and will error on versions not found. To test against only a single version of Python, specify the version at the tox command line. For example, to test only Python 2.7:

tox -e py27

Multiple versions may be specified, separated by a comma:

tox -e py27,py35

Documentation generation and code style checking are not performed by default, and so must be explicitly provided to the tox command. Documentation generation requires either Python 2.7, or Python 3.3 or greater.

tox -e docs,style


This software is open-source software. Copyright Digi International, 2015.

This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, you can obtain one at

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