Building conda packages on Windows

This tutorial describes how to use conda build to create conda packages on the Windows operating system, using the examples of SEP and pySLALIB.

The final built packages from this tutorial are available on Anaconda Cloud:

This tutorial also describes writing recipes. You can see the final SEP recipe and the pySLALIB recipe on GitHub in the conda documentation repository.

Before you start

Before you start, check the prerequisites.


Microsoft Visual Studio

In the standard practices of the conda developers, conda packages for different versions of Python are each built with their own version of Visual Studio (VS):

  • Python 2.7 packages with Visual Studio 2008
  • Python 3.4 packages with VS 2010
  • Python 3.5 packages with VS 2015
  • Python 3.6 packages with VS 2015

Using these versions of VS to build packages for each of these versions of Python is also the practice used for the official builds of Python. Currently VS 2008 and VS 2010 are available only through resellers, while VS 2015 can be purchased online from Microsoft.

Alternatives to Microsoft Visual Studio

There are free alternatives available for each version of the VS compilers:

The MS Visual C++ Compiler for Python 2.7 and the Microsoft Windows SDK for Windows 7 and .NET Framework 4 are both reasonably well tested. Conda build is carefully tested to support these configurations, but there are known issues with the CMake build tool and these free VS 2008 and 2010 alternatives. In these cases, you should prefer the “NMake Makefile” generator, rather than a Visual Studio solution generator.

Windows versions

You can use any recent version of Windows. These examples were built on Windows 8.1.

Other tools

Some environments initially lack tools such as bzip2 or Git that may be needed for some build workflows.

Git is available through conda: conda install git

You can obtain bzip2 the same way. The conda bzip2 package includes only the bzip2 library and not the bzip2 executable, so some users may need to install the bzip2 executable from another source such as Place this executable somewhere on PATH. One good option is to place it in your Miniconda/Anaconda install path, in the Library/bin folder.

Developing a build strategy

Conda recipes are typically built with a trial-and-error method. Often the first attempt to build a package fails with compiler or linker errors, often caused by missing dependencies. The person writing the recipe then examines these errors and modifies the recipe to include the missing dependencies, usually as part of the meta.yaml file. Then the recipe writer attempts the build again, and after a few of these cycles of trial and error, the package builds successfully.

Building with a Python version different from your Miniconda installation

Miniconda2 and Miniconda3 can each build packages for either Python 2 or Python 3 simply by specifying the version you want. Miniconda2 includes only Python 2, and Miniconda3 includes only Python 3.

Installing only one makes it easier to keep track of the builds, but it is possible to have both installed on the same system at the same time. If you have both installed, use the where command to see which version comes first on PATH since this is the one you will be using:

where python

To build a package for a Python version other than the one in your Miniconda installation, use the --python option in the conda-build command.

EXAMPLE: To build a Python 3.5 package with Miniconda2:

conda-build recipeDirectory --python=3.5

NOTE: Replace recipeDirectory with the name and path of your recipe directory.

Automated testing

After the build, if the recipe directory contains a test file named run_test.bat on Windows, or on macOS or Linux, or on any platform, the file runs to test the package, and any errors are reported.

NOTE: Use the Test section of the meta.yaml file to move data files from the recipe directory to the test directory when the test is run.

Building a SEP package with conda and Python 2 or 3

The SEP documentation states that SEP runs on Python 2 and 3, and it depends only on NumPy. Searching for SEP and PyPI shows that there is already a PyPI package for SEP.

Because a PyPI package for SEP already exists, the conda skeleton command can make a skeleton or outline of a conda recipe based on the PyPI package. Then the recipe outline can be completed manually, and conda can build a conda package from the completed recipe.

Install Visual Studio

If you have not already done so, install the appropriate version of Visual Studio:

  • For Python 3—Visual Studio 2015:
    1. Choose Custom install.
    2. Under Programming Languages, choose to install Visual C++ .
  • For Python 2—Visual Studio 2008:
    1. Choose Custom install.
    2. Choose to install X64 Compilers and Tools. Install Service Pack 1.

Make a conda skeleton recipe

  1. Run the skeleton command:

    conda skeleton pypi sep

    The skeleton command installs into a newly created directory called sep.

  2. Go to the sep directory to view the files:

    cd sep

    Three skeleton files have been created:

    • bld.bat for Windows.
    • for macOS/Linux.
    • meta.yaml for all platforms.

Edit the skeleton files

For this package, bld.bat and need no changes. You need to edit the meta.yaml file to add the dependency on NumPy and add an optional test for the built package by importing it.

  1. In the requirements section of the meta.yaml file, add a line that adds NumPy as a requirement to build the package.
  2. Add a second line to list NumPy as a requirement to run the package.

Set the NumPy version to the letters x.x.

Make sure the new line is aligned with - python on the line above it.


    - python
    - numpy     x.x

    - python
    - numpy     x.x

NOTE: Using the letters x.x instead of a specific version such as 1.11 pins NumPy dynamically, so that the actual version of NumPy is taken from the build command. Currently NumPy is the only package that can be pinned dynamically. Pinning is important for SEP because this package uses NumPy’s C API through Cython. That API changes between NumPy versions, so it is important to use the same NumPy version at runtime that was used at build time.

Optional—Add a test for the built package

Adding this optional test will test the package at the end of the build by making sure that the Python statement import sep runs successfully:

  1. In the test section, remove the # used to comment out the lines test: and imports:.
  2. Add - sep, checking to be sure that the indentation is consistent with the rest of the file.


  # Python imports
    - sep

Create a test file

Make a new test file called containing the following code adapted from Background estimation and source detection, and save it to the sep directory:

import numpy as np
import sep

data = np.random.random((256, 256))

# Measure a spatially variable background of some image data
# (a numpy array)
bkg = sep.Background(data)

# ... or with some optional parameters
# bkg = sep.Background(data, mask=mask, bw=64, bh=64, fw=3, fh=3)

After the build, this file is run to test the newly built package.

Now the recipe is complete.

Build the package

Build the package using the recipe you just created:

conda-build . --numpy=1.11

Check the output

  1. Check the output to make sure that the build completed successfully. The output contains the location of the final package file and a command to upload the package to Anaconda Cloud.
  2. If there are any linker or compiler errors, modify the recipe and build again.

Building a pySLALIB package with conda and Python 2 or 3

This procedure describes how to build a package with Python 2 or Python 3. Follow the instructions for the version that you want to build with.

Because pySLALIB includes Fortran, building it requires a Fortran compiler. Because there is no PyPI package for pySLALIB, you cannot use a skeleton recipe generated by using conda skeleton. You must create the recipe from scratch. The steps to build pySLALIB are similar to the steps to build SEP, but they also include installing the Fortran compiler, writing meta.yaml to fetch the package from GitHub instead of PyPI and applying the correct patches to the Fortran code.

To build a pySLALIB package:

  1. Install Visual Studio:

    • For Python 3, install Visual Studio 2015. Choose Custom install. Under Programming Languages, choose to install Visual C++.
    • For Python 2, install Visual Studio 2008. Choose Custom install. Choose to install X64 Compilers and Tools. Install Visual Studio 2008 Service Pack 1.
  2. Install Intel Parallel Studio Composer Edition. Go to the Intel Fortran Compilers page. Choose Try & Buy. Choose Parallel Studio Composer Edition for Windows. You may choose the version with Fortran only instead of the version with Fortran and C++. There is a free 30-day trial available. Fill out the form, including your email address. Intel will email you a download link.

    • For Python 3, download and install Intel Parallel Studio XE Composer Edition for Fortran Windows.
    • For Python 2, open the download page for Intel Parallel Studio XE Composer Edition for Fortran Windows. Select Additional downloads, latest updates and prior versions. Select version 2013 Update 6. This is Intel Visual Fortran Composer XE 2013 SP1 (compiler version 14.0), the most recent Intel Fortran compiler that works with Visual Studio 2008. Choose Download Now and install this version.
  3. Install Git. Because the pySLALIB package sources are retrieved from GitHub for the build, you must install Git:

    conda install git
  4. Make a recipe. You can write a recipe from scratch, or use the recipe we wrote. This recipe contains 4 files:

    • meta.yaml sets the GitHub location of the pySLALIB files and how the system will apply the intel_fortran_use.patch.
    • bld.bat is a Windows batch script that ensures that the correct 32-bit or 64-bit libraries are linked during the build and runs the build.
    • is a test adapted from the one in the pySLALIB GitHub repository to check that the build completed successfully.
    • intel_fortran_use.patch is a patch to the pySLALIB Fortran code so that it works with the Intel Fortran compiler.
  5. In your home directory, create a recipe directory named pyslalib and copy in the 4 files mentioned in the previous step.

  6. Build the package.

    • For Python 3, in the Apps menu, under Intel Parallel Studio XE 2016, open the Compiler 16.0 Update 3 for Intel 64 Visual Studio 2015 environment command prompt.
    • For Python 2, in the Apps menu, under Intel Parallel Studio XE 2013, open the Intel 64 Visual Studio 2008 mode command prompt.
  7. Run conda-build, using the correct path name of the recipe directory, including your correct user name. In this example, the user name is “builder”:

    conda-build C:\Users\builder\pyslalib
  8. Check the output to make sure the build completed successfully. The output also contains the location of the final package file and a command to upload the package to Cloud.

  9. In case of any linker or compiler errors, modify the recipe and run it again.