Frequently Asked Questions

Problems with running frozen programs

A common problem is that cx_Freeze hasn’t automatically detected that a file needs to be copied. Modules that your code imports are detected, but if they’re dynamically loaded - e.g. by a plugin system - you have to tell cx_Freeze about them. This is easy using a setup script:

  • For Python code, specify the module names in the includes or packages options.
  • List compiled libraries (.dll or .so files) in the include_files option.
  • Data files are a bit more complex - see Using data files.

Windows command prompt appears briefly

If there’s a problem with your frozen application, you may see a command prompt window appear briefly when you try to run it, and then disappear again. This happens when a console-mode executable exits quickly, usually if there’s an error as soon as it starts.

There are two ways to debug what’s going on:

  1. Freeze your application with the Win32GUI base (see distutils setup script or cxfreeze script). This doesn’t use a console window, and reports errors in a dialog box.
  2. Alternatively, start a command prompt yourself and launch the frozen executable from the command line. This will let you see any error messages in the console.

Freezing for other platforms

cx_Freeze works on Windows, Mac and Linux, but on each platform it only makes an executable that runs on that platform. So if you want to freeze your program for Windows, freeze it on Windows; if you want to run it on Macs, freeze it on a Mac.

At a pinch, you can try to make a Windows executable using Wine. Our experience is that you need to copy some files in manually after cx_Freeze has run to make the executable work. We don’t recommend this option.

Using data files

Applications often need data files besides the code, such as icons. Using a setup script, you can list data files or directories in the include_files option to build_exe. They’ll be copied to the build directory alongside the executable. Then to find them, use code like this:

def find_data_file(filename):
    if getattr(sys, 'frozen', False):
        # The application is frozen
        datadir = os.path.dirname(sys.executable)
        # The application is not frozen
        # Change this bit to match where you store your data files:
        datadir = os.path.dirname(__file__)

    return os.path.join(datadir, filename)

An alternative is to embed data in code, for example by using Qt’s resource system.

Microsoft Visual C++ Redistributable Package

Python on Windows requires the Microsoft Visual C++ Redistributable Package. Python 2.6-3.2 uses the 2008 version, and because of how this is installed, cx_Freeze doesn’t automatically copy it for your application. It’s also not clear whether everyone has the right to redistribute the DLLs. You’re responsible for checking the license conditions associated with the DLLs you have installed.

  • If your license allows you to distribute these files, specify the include_msvcr option to build_exe to have them distributed automatically.

  • If not, your users or your installer will need to install the Microsoft Visual C++ Redistributable Package (a free download from Microsoft). It’s not uncommon for this to already be present on modern computers, but it’s not, as far as we know, part of a standard Windows installation. Note that the “SP1” version of this does not work – it has to exactly match the version which Python itself is compiled with.

Up to Python 2.5, and again from Python 3.3, the MSVCR DLLs are installed in a normal location, and cx_Freeze will copy them automatically. It’s still up to you to ensure that the licenses of all the files you use allow you to distribute them as part of your application.

Single-file executables

cx_Freeze does not support building a single file exe, where all of the libraries for your application are embedded in one executable file.

You can use IExpress to compress the build directory from cx_Freeze into a self-extracting archive: an exe which unpacks your application into a temporary directory and runs it. IExpress is a utility that’s included with Windows, intended for making installers, but it works equally well if you tell it to run the cx_Freeze-built exe after extraction.

Alternatively, you can create a self extracting archive using 7zip. This is a bit more complex than using IExpress, but might provide more flexibility, and allows you to build your application using only open source tools.