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A mongo mocking library with an ephemeral MongoDB running in memory.



[ PyPI ][ GitHub ][ BETA Docs]


A mongo mocking library with an ephemeral MongoDB running in memory.

What's new?


  • Tooling enhancements. [PR #90]
  • Configuration for data directory. [PR #90]
  • Configuration for data directory. [PR #90]


  • Development version upped to Python 3.9
  • Update to build system. Contribution by @pbsds
  • Coercing boolean configs correctly. Issue #82


pip install pymongo-inmemory



There are several ways you can configure pymongo_inmemory.

  1. Insert a new section titled pymongo_inmemory to your project's setup.cfg version you want to spin up:
    operating_system = ubuntu
    os_version = 18
    mongod_port = 27019
  2. Define an ALL_CAPS environment variables with prefix PYMONGOIM__ (attention to trailing double underscores.) For instance, to override the port, set up an environment variable PYMONGOIM__MONGOD_PORT.

Import and use

pymongo_inmemory wraps the client class MongoClient that comes from pymongo and configures with an ephemeral MongoDB server. You can import this MongoClient from pymongo_inmemory instead of pymongo and use it to perform tests:

from pymongo_inmemory import MongoClient

client = MongoClient()  # No need to provide host
db = client['testdb']
collection = db['test-collection']
# etc., etc.

# Also usable with context manager
with MongoClient() as client:
    # do stuff


Config parameterDescriptionDefault
mongo_versionWhich MongoD version to download and use.Latest for the OS
mongod_portOverride port preference.Automatically picked between 27017 and 28000 after testing availability
operating_systemThis makes sense for Linux setting, where there are several flavoursAutomatically determined (Generic for Linux)*
os_versionIf an operating system has several versions use this parameter to select oneLatest version of the OS will be selected from the list
download_urlIf set, it won't attempt to determine which MongoDB to download. However there won't be a fallback either.Automatically determined from given parameters and using internal URL bank**
ignore_cacheEven if there is a downloaded version in the cache, download it again.False
use_local_mongodIf set, it will try to use a local mongod instance instead of downloading one.False
download_folderOverride the default download location.pymongo_inmemory/.cache/download
extract_folderOverride the default extraction location.pymongo_inmemory/.cache/extract
NEWmongod_data_folderProvide a data folder to be used by MongoD.A TemporaryDirectory will be used
NEWmongo_client_hostHostname or connection string
NEWdbnameProvide a database name to connect'pimtest'
  • *Note 1: Generic Linux version offering for MongoDB ends with version 4.0.23. If the operating system is just linux and if selected MongoDB version is higher, it will default to 4.0.23.
  • *Note 2:*** URL bank is filled with URLs collected from release list and archived released list, so if a version is not in the bank you can use the same list to provide an official download link.

Available MongoDB versions

There is an internal URL bank that is filled with URLs collected from

Below table is a summary of possible setting for operating_system, os_version and available MongoDB versions for them to set as mongo_version at major.minor level.

Note that, not all major.minor.patch level is available for all OS versions. For exact patch level range, either see release pages of MongoDB or have a look at the internal URL bank.

operating_systemos_versionMongoDB versions (major.minor)
amazon13.6, 3.2, 3.4, 4.2, 5.0, 4.0, 3.0, 4.4
amazon27.0, 6.0, 3.6, 5.0, 4.2, 4.0, 4.4
debian73.6, 3.0, 3.2, 3.4
debian83.6, 4.0, 3.2, 3.4
debian93.6, 5.0, 4.2, 4.0, 4.4
debian104.2, 5.0, 6.0, 4.4
debian117.0, 6.0, 5.0
rhel53.0, 3.2
rhel63.6, 3.2, 3.4, 4.2, 4.0, 3.0, 4.4
rhel77.0, 6.0, 3.6, 3.2, 3.4, 4.2, 5.0, 4.0, 3.0, 4.4
rhel87.0, 6.0, 3.6, 5.0, 4.2, 4.0, 4.4
rhel97.0, 6.0
NEWrhel-arm85.0, 7.0, 6.0, 4.4
NEWrhel-arm97.0, 6.0
suse113.6, 3.0, 3.2, 3.4
suse127.0, 6.0, 3.6, 3.2, 3.4, 4.2, 5.0, 4.0, 4.4
suse157.0, 6.0, 5.0, 4.2, 4.4
ubuntu123.6, 3.0, 3.2, 3.4
ubuntu143.6, 3.2, 3.4, 4.0, 3.0
ubuntu163.6, 3.2, 3.4, 4.2, 4.0, 4.4
ubuntu186.0, 3.6, 5.0, 4.2, 4.0, 4.4
ubuntu205.0, 7.0, 6.0, 4.4
ubuntu227.0, 6.0
NEWubuntu-arm205.0, 7.0, 6.0, 4.4
NEWubuntu-arm227.0, 6.0
linuxgeneric3.6, 3.2, 3.4, 2.6, 4.0, 3.0
osxgeneric7.0, 6.0, 3.6, 3.2, 3.4, 4.2, 5.0, 2.6, 4.0, 3.0, 4.4
NEWmacosarm7.0, 6.0
sunos53.0, 2.6, 3.2, 3.4
windowsgeneric7.0, 6.0, 3.6, 3.2, 3.4, 4.2, 5.0, 2.6, 4.0, 3.0, 4.4

*Note: No need to specify generic, as it will be chosen automatically since it's the only version for that OS.

How do we determine which MongoDB to download?

There are two (three if it's a Linux flavour) bits of information we need to determine a MongoDB: operating system and MongoDB version.

Note: You can always set download_url to provide an exact URL to download from.

Operating System detection

Python has limited tools in its standard library to determine the exact version of the operating system and operating system version. pymongo_inmemory basically reads output of platform.system() to determine if underlying OS is Linux, MacOS or Windows.

For Windows and MacOS, it will download only one flavour of OS for a particular MongoDB version (64bit and, for Windows, Windows Server version if there is one.) However, Linux has many flavours. Up to MongoDB 4.0.23, a MongoDB for a generic Linux OS can still be downloaded, but for later versions of MongoDB, there are no such builds, hence you will need to explicitly set operating_system parameter if you want to use MongoDB versions higher than that.

Operating system detection behaviour of pymongo_inmemory might change in the future, if there is a demand for more magic, but for now we are keeping things simple.

Deciding MongoDB version
  • If no version is provided, highest version of MongoDB for the operating system is selected.
  • If only a major version is given, like 4, then highest minor.patch version is selected, like 4.4.4.
  • If only major.minor version is given, like 4.0, then highest patch version is selected, like 4.0.23.
  • If exact major.minor.patch version is given, like 4.0.22, then that version is selected.
  • If patch version is not found. like 4.0.50, highest patch version is selected, like 4.0.23.
  • If minor version is not found. like 3.90.50, highest minor.patch version is selected, like 3.6.22.
  • If major version is not found. like 1.0.0, highest major.minor.patch version is selected, like 4.4.4.

Supported Python versions

Since few development tools only support Python version 3.9 and above, all testing and tooling done from that version up.

This also limits the minimum Python version of tested features. However there shouldn't be a hard limitation to use Python 3.5. We recommend upgrading older Python versions than that.


Project is set up to develop with poetry. We rely on pyenv to maintain the minimum supported Python version.

After installing pyenv, poetry, and cloning the repo, create the shell and install all package requirements:

pyenv install --skip-existing
poetry install --no-root
poetry shell

Run the tests:


If on NIX systems you can run further tests:

bash tests/integrity/

Adding a new MongoDB version

Follow the guide here.

See how you can wet your feet

Check out good first issues.



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