Using Spec Files

When you execute

pyinstaller options..

the first thing PyInstaller does is to build a spec (specification) file myscript.spec. That file is stored in the --specpath= directory, by default the current directory.

The spec file tells PyInstaller how to process your script. It encodes the script names and most of the options you give to the pyinstaller command. The spec file is actually executable Python code. PyInstaller builds the app by executing the contents of the spec file.

For many uses of PyInstaller you do not need to examine or modify the spec file. It is usually enough to give all the needed information (such as hidden imports) as options to the pyinstaller command and let it run.

There are four cases where it is useful to modify the spec file:

  • When you want to bundle data files with the app.
  • When you want to include run-time libraries (.dll or .so files) that PyInstaller does not know about from any other source.
  • When you want to add Python run-time options to the executable.
  • When you want to create a multiprogram bundle with merged common modules.

These uses are covered in topics below.

You create a spec file using this command:

pyi-makespec options [other scripts …]

The options are the same options documented above for the pyinstaller command. This command creates the name.spec file but does not go on to build the executable.

After you have created a spec file and modified it as necessary, you build the application by passing the spec file to the pyinstaller command:

pyinstaller options name.spec

When you create a spec file, most command options are encoded in the spec file. When you build from a spec file, those options cannot be changed. If they are given on the command line they are ignored and replaced by the options in the spec file.

Only the following command-line options have an effect when building from a spec file:

  • --upx-dir=
  • --distpath=
  • --workpath=
  • --noconfirm
  • --ascii
  • --clean

Spec File Operation

After PyInstaller creates a spec file, or opens a spec file when one is given instead of a script, the pyinstaller command executes the spec file as code. Your bundled application is created by the execution of the spec file. The following is an shortened example of a spec file for a minimal, one-folder app:

block_cipher = None
a = Analysis([''],
pyz = PYZ(a.pure, a.zipped_data,
exe = EXE(pyz,... )
coll = COLLECT(...)

The statements in a spec file create instances of four classes, Analysis, PYZ, EXE and COLLECT.

  • A new instance of class Analysis takes a list of script names as input. It analyzes all imports and other dependencies. The resulting object (assigned to a) contains lists of dependencies in class members named:
    • scripts: the python scripts named on the command line;
    • pure: pure python modules needed by the scripts;
    • binaries: non-python modules needed by the scripts, including names given by the --add-binary option;
    • datas: non-binary files included in the app, including names given by the --add-data option.
  • An instance of class PYZ is a .pyz archive (described under Inspecting Archives below), which contains all the Python modules from a.pure.
  • An instance of EXE is built from the analyzed scripts and the PYZ archive. This object creates the executable file.
  • An instance of COLLECT creates the output folder from all the other parts.

In one-file mode, there is no call to COLLECT, and the EXE instance receives all of the scripts, modules and binaries.

You modify the spec file to pass additional values to Analysis and to EXE.

Adding Files to the Bundle

To add files to the bundle, you create a list that describes the files and supply it to the Analysis call. When you bundle to a single folder (see Bundling to One Folder), the added data files are copied into the folder with the executable. When you bundle to a single executable (see Bundling to One File), copies of added files are compressed into the executable, and expanded to the _MEIxxxxxx temporary folder before execution. This means that any changes a one-file executable makes to an added file will be lost when the application ends.

In either case, to find the data files at run-time, see Run-time Information.

Adding Data Files

You can add data files to the bundle by using the --add-data command option, or by adding them as a list to the spec file.

When using the spec file, provide a list that describes the files as the value of the datas= argument to Analysis. The list of data files is a list of tuples. Each tuple has two values, both of which must be strings:

  • The first string specifies the file or files as they are in this system now.
  • The second specifies the name of the folder to contain the files at run-time.

For example, to add a single README file to the top level of a one-folder app, you could modify the spec file as follows:

a = Analysis(...
     datas=[ ('src/README.txt', '.') ],

And the command line equivalent (see What to bundle, where to search for platform-specific details):

pyinstaller --add-data 'src/README.txt:.'

You have made the datas= argument a one-item list. The item is a tuple in which the first string says the existing file is src/README.txt. That file will be looked up (relative to the location of the spec file) and copied into the top level of the bundled app.

The strings may use either / or \ as the path separator character. You can specify input files using “glob” abbreviations. For example to include all the .mp3 files from a certain folder:

a = Analysis(...
     datas= [ ('/mygame/sfx/*.mp3', 'sfx' ) ],

All the .mp3 files in the folder /mygame/sfx will be copied into a folder named sfx in the bundled app.

The spec file is more readable if you create the list of added files in a separate statement:

added_files = [
         ( 'src/README.txt', '.' )
         ( '/mygame/sfx/*.mp3', 'sfx' ),
    a = Analysis(...
         datas = added_files,

You can also include the entire contents of a folder:

added_files = [
         ( 'src/README.txt', '.' )
         ( '/mygame/data', 'data' ),
         ( '/mygame/sfx/*.mp3', 'sfx' ),

The folder /mygame/data will be reproduced under the name data in the bundle.

Using Data Files from a Module

If the data files you are adding are contained within a Python module, you can retrieve them using pkgutils.get_data().

For example, suppose that part of your application is a module named helpmod. In the same folder as your script and its spec file you have this folder arrangement:


Because your script includes the statement import helpmod, PyInstaller will create this folder arrangement in your bundled app. However, it will only include the .py files. The data file help_data.txt will not be automatically included. To cause it to be included also, you would add a datas tuple to the spec file:

a = Analysis(...
     datas= [ ('helpmod/help_data.txt', 'helpmod' ) ],

When your script executes, you could find help_data.txt by using its base folder path, as described in the previous section. However, this data file is part of a module, so you can also retrieve its contents using the standard library function pkgutil.get_data():

import pkgutil
help_bin = pkgutil.get_data( 'helpmod', 'help_data.txt' )

In Python 3, this returns the contents of the help_data.txt file as a binary string. If it is actually characters, you must decode it:

help_utf = help_bin.decode('UTF-8', 'ignore')

Adding Binary Files


Binary files refers to DLLs, dynamic libraries, shared object-files, and such, which PyInstaller is going to search for further binary dependencies. Files like images and PDFs should go into the datas.

You can add binary files to the bundle by using the --add-binary command option, or by adding them as a list to the spec file. In the spec file, make a list of tuples that describe the files needed. Assign the list of tuples to the binaries= argument of Analysis.

Normally PyInstaller learns about .so and .dll libraries by analyzing the imported modules. Sometimes it is not clear that a module is imported; in that case you use a --hidden-import= command option. But even that might not find all dependencies.

Suppose you have a module that is written in C and uses the Python C-API. Your program imports special_ops, and PyInstaller finds and includes But perhaps links to libiodbc.2.dylib. PyInstaller does not find this dependency. You could add it to the bundle this way:

a = Analysis(...
         binaries=[ ( '/usr/lib/libiodbc.2.dylib', '.' ) ],

Or via the command line (again, see What to bundle, where to search for platform-specific details):

pyinstaller --add-binary '/usr/lib/libiodbc.2.dylib:.'

As with data files, if you have multiple binary files to add, create the list in a separate statement and pass the list by name.

Advanced Methods of Adding Files

PyInstaller supports a more advanced (and complex) way of adding files to the bundle that may be useful for special cases. See The TOC and Tree Classes below.

Giving Run-time Python Options

You can pass command-line options to the Python interpreter. The interpreter takes a number of command-line options but only the following are supported for a bundled app:

  • v to write a message to stdout each time a module is initialized.
  • u for unbuffered stdio.
  • W and an option to change warning behavior: W ignore or W once or W error.

To pass one or more of these options, create a list of tuples, one for each option, and pass the list as an additional argument to the EXE call. Each tuple has three elements:

  • The option as a string, for example v or W ignore.
  • None
  • The string OPTION

For example modify the spec file this way:

options = [ ('v', None, 'OPTION'), ('W ignore', None, 'OPTION') ]
a = Analysis( ...
exe = EXE(pyz,
      options,   <--- added line

Spec File Options for a Mac OS X Bundle

When you build a windowed Mac OS X app (that is, running in Mac OS X, you specify the --onefile --windowed options), the spec file contains an additional statement to create the Mac OS X application bundle, or app folder:

app = BUNDLE(exe,

The icon= argument to BUNDLE will have the path to an icon file that you specify using the --icon= option. The bundle_identifier will have the value you specify with the --osx-bundle-identifier= option.

An Info.plist file is an important part of a Mac OS X app bundle. (See the Apple bundle overview for a discussion of the contents of Info.plist.)

PyInstaller creates a minimal Info.plist. You can add or overwrite entries in the plist by passing an info_plist= parameter to the BUNDLE call. The value of this argument is a Python dict. Each key and value in the dict becomes a key and value in the Info.plist file. For example, when you use PyQt5, you can set NSHighResolutionCapable to True to let your app also work in retina screen:

app = BUNDLE(exe,
            'NSHighResolutionCapable': 'True'

The info_plist= parameter only handles simple key:value pairs. It cannot handle nested XML arrays. For example, if you want to modify Info.plist to tell Mac OS X what filetypes your app supports, you must add a CFBundleDocumentTypes entry to Info.plist (see Apple document types). The value of that keyword is a list of dicts, each containing up to five key:value pairs.

To add such a value to your app’s Info.plist you must edit the plist file separately after PyInstaller has created the app. However, when you re-run PyInstaller, your changes will be wiped out. One solution is to prepare a complete Info.plist file and copy it into the app after creating it.

Begin by building and testing the windowed app. When it works, copy the Info.plist prepared by PyInstaller. This includes the CFBundleExecutable value as well as the icon path and bundle identifier if you supplied them. Edit the Info.plist as necessary to add more items and save it separately.

From that point on, to rebuild the app call PyInstaller in a shell script, and follow it with a statement such as:

cp -f Info.plist dist/

Multipackage Bundles


This feature is broken in the PyInstaller 3.0 release. Do not attempt building multipackage bundles until the feature is fixed. If this feature is important to you, follow and comment on PyInstaller Issue #1527.

Some products are made of several different apps, each of which might depend on a common set of third-party libraries, or share code in other ways. When packaging such an product it would be a pity to treat each app in isolation, bundling it with all its dependencies, because that means storing duplicate copies of code and libraries.

You can use the multipackage feature to bundle a set of executable apps so that they share single copies of libraries. You can do this with either one-file or one-folder apps. Each dependency (a DLL, for example) is packaged only once, in one of the apps. Any other apps in the set that depend on that DLL have an “external reference” to it, telling them to extract that dependency from the executable file of the app that contains it.

This saves disk space because each dependency is stored only once. However, to follow an external reference takes extra time when an app is starting up. All but one of the apps in the set will have slightly slower launch times.

The external references between binaries include hard-coded paths to the output directory, and cannot be rearranged. If you use one-folder mode, you must install all the application folders within a single parent directory. If you use one-file mode, you must place all the related applications in the same directory when you install the application.

To build such a set of apps you must code a custom spec file that contains a call to the MERGE function. This function takes a list of analyzed scripts, finds their common dependencies, and modifies the analyses to minimize the storage cost.

The order of the analysis objects in the argument list matters. The MERGE function packages each dependency into the first script from left to right that needs that dependency. A script that comes later in the list and needs the same file will have an external reference to the prior script in the list. You might sequence the scripts to place the most-used scripts first in the list.

A custom spec file for a multipackage bundle contains one call to the MERGE function:


MERGE is used after the analysis phase and before EXE and COLLECT. Its variable-length list of arguments consists of a list of tuples, each tuple having three elements:

  • The first element is an Analysis object, an instance of class Analysis, as applied to one of the apps.
  • The second element is the script name of the analyzed app (without the .py extension).
  • The third element is the name for the executable (usually the same as the script).

MERGE examines the Analysis objects to learn the dependencies of each script. It modifies these objects to avoid duplication of libraries and modules. As a result the packages generated will be connected.

Example MERGE spec file

One way to construct a spec file for a multipackage bundle is to first build a spec file for each app in the package. Suppose you have a product that comprises three apps named (because we have no imagination) foo, bar and zap:

pyi-makespec options as appropriate…

pyi-makespec options as appropriate…

pyi-makespec options as appropriate…

Check for warnings and test each of the apps individually. Deal with any hidden imports and other problems. When all three work correctly, combine the statements from the three files foo.spec, bar.spec and zap.spec as follows.

First copy the Analysis statements from each, changing them to give each Analysis object a unique name:

foo_a = Analysis([''],

bar_a = Analysis([''], etc., etc...

zap_a = Analysis([''], etc., etc...

Now call the MERGE method to process the three Analysis objects:

MERGE( (foo_a, 'foo', 'foo'), (bar_a, 'bar', 'bar'), (zap_a, 'zap', 'zap') )

The Analysis objects foo_a, bar_a, and zap_a are modified so that the latter two refer to the first for common dependencies.

Following this you can copy the PYZ, EXE and COLLECT statements from the original three spec files, substituting the unique names of the Analysis objects where the original spec files have a., for example:

foo_pyz = PYZ(foo_a.pure)
foo_exe = EXE(foo_pyz, foo_a.scripts, ... etc.
foo_coll = COLLECT( foo_exe, foo_a.binaries, foo_a.datas... etc.

bar_pyz = PYZ(bar_a.pure)
bar_exe = EXE(bar_pyz, bar_a.scripts, ... etc.
bar_coll = COLLECT( bar_exe, bar_a.binaries, bar_a.datas... etc.

(If you are building one-file apps, there is no COLLECT step.) Save the combined spec file as foobarzap.spec and then build it:

pyi-build foobarzap.spec

The output in the dist folder will be all three apps, but the apps dist/bar/bar and dist/zap/zap will refer to the contents of dist/foo/ for shared dependencies.

There are several multipackage examples in the PyInstaller distribution folder under /tests/old_suite/multipackage.

Remember that a spec file is executable Python. You can use all the Python facilities (for and with and the members of sys and io) in creating the Analysis objects and performing the PYZ, EXE and COLLECT statements. You may also need to know and use The TOC and Tree Classes described below.

Globals Available to the Spec File

While a spec file is executing it has access to a limited set of global names. These names include the classes defined by PyInstaller: Analysis, BUNDLE, COLLECT, EXE, MERGE, PYZ, TOC and Tree, which are discussed in the preceding sections.

Other globals contain information about the build environment:

The relative path to the dist folder where the application will be stored. The default path is relative to the current directory. If the --distpath= option is used, DISTPATH contains that value.
The absolute path to the PyInstaller distribution, typically in the current Python site-packages folder.
The complete spec file argument given to the pyinstaller command, for example myscript.spec or source/myscript.spec.
The path prefix to the SPEC value as returned by os.path.split().
The name of the spec file, for example myscript.
The path to the build directory. The default is relative to the current directory. If the workpath= option is used, workpath contains that value.
The full path to the warnings file in the build directory, for example build/warnmyscript.txt.