Installing Z3 in an environment on a Windows 10 (x64) system

4 minute read

What is Z3?

As per the horse’s mouth in this tutorial:

Z3 is a state-of-the art theorem prover from Microsoft Research. It can be used to check the satisfiability of logical formulas over one or more theories. Z3 offers a compelling match for software analysis and verification tools, since several common software constructs map directly into supported theories.

Z3 is also a problem solver as shown in numerous examples in Dennis Yurichev’s SAT/SMT by example booklet. Better yet: there is a python wrapper for Z3!

Installing Z3 for python on Windows 10

These are the steps I followed for a successful installation of Z3 on my current system, Windows 10 x64. I used two sources indicated in brackets: the Z3 README file (RM) and addtional instructions from issue #916.

Step 0. Clone the source code [RM]:

cd <a path>
git clone

The path <build> I refer henceforth is equivalent to <a path>\z3\build.

Step 1. First build: to .pyc components [916]:

The build operation should take place inside the x64 Native Build Tools Prompt. For my system, the VS Tools version (Windows 10) is “x64 Native Tools Command Prompt for VS 2017”

Open that command prompt, enter the following command and press ENTER:

python scripts/ -x --python

Step If sucessful, the last few lines of the stdout will be:

64-bit:         True
Writing build\Makefile
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Copied Z3Py example '' to 'build\python'
Makefile was successfully generated.
  compilation mode: Release
  platform: x64

To build Z3, open a [VS Tools x64 Command Prompt], then type 'cd <build> && nmake'

Remark: to open a Visual Studio Command Prompt, go to:  
"Start > All Programs > Visual Studio > Visual Studio Tools"

Step 1.2 Following instructions from Step above:

Typed: cd <build> && nmake, then pressed ENTER. This command compiles the C++ code.

Step 2. Add Z3 exec and lib files to the PATH [916]:

The z3.exe appears to be independent and can work anywhere […]. So you can copy both build/z3.exe and build/libz3.dll into somewhere [and add them to] the PATH.

I created this folder C:\Program Files\z3, copied z3.exe and libz3.dll from <build> into it, and created the PATH variables: (z3, C:\Program Files\Z3\z3.exe) and (libz3, C:\Program Files\Z3\libz3.dll) in both the System and User variables paths.

Step 3. Copy the build/python/z3 directory to an environment:

#916: Then the build/python/z3 directory should be copied into the site-packages directory of Python. On Windows, this isn’t done automatically, instead you have to find your Windows site-packages: like python3 -c ‘import site; print(site.getsitepackages())’, then copy the entire directory there.

Step 3.1: Get the site packages path for an environment:

I activated my chosen environment env1, which uses py3.6.7, launched python and used the code from [916].

Step 3.2: Copied build/python/z3 directory to <env1>\lib\\site-packages

Step 4. Tests:

S4.1 Test 1:

Using a conda prompt, I activated <env1>, launched python & imported z3:

(env1)> python
>>> import z3   ##Import error:
Could not find libz3.dll; consider adding the directory containing it to
  - your system's PATH environment variable,
  - the Z3_LIBRARY_PATH environment variable, or
  - to the custom Z3_LIBRARY_DIRS Python-builtin before importing the z3 module, e.g. via
    import builtins
    builtins.Z3_LIB_DIRS = [ '/path/to/libz3.dll' ]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "env1\lib\site-packages\z3\", line 1, in <module>
    from .z3 import *
  File "env1\lib\site-packages\z3\", line 45, in <module>
    from . import z3core
  File "env1\lib\site-packages\z3\", line 67, in <module>
    raise Z3Exception("libz3.%s not found." % _ext)
z3.z3types.Z3Exception: libz3.dll not found.

Step 4.2 Test 2:

Fix: I copied the build/python/libz3.dll file into the <env1>\lib\\site-packages\z3 folder and repeated the import & variable tests:

(base)> conda activate env1
(env1)> python
>>> import z3
>>> z3.Int('x')
>>> exit()
(env1)> conda deactivate


What I think happened can be seen using the path from the sys module:

>>> import sys; sys.path
['', '<env1>\\', '<env1>\\DLLs', '<env1>\\lib', '<env1>', '<env1>\\lib\\site-packages']

Since env1 is the active environment, this is the default path, so until I copied libz3.dll into <env1>\lib\\site-packages\z3, it could not be found.

Time play with!