Pop's build system, used to build python projects

## Intro

Pop-Build is the single binary builder for pop projects. While it is written with the intention of supporting pop projects it can be used with any python project.

## Getting Started

The main idea behind Pop-Build is to make building python projects as a single frozen binary easy. Therefore using pop-build just takes a few steps.

So we can start with an existing python application, this quickstart will assume that your python project has a standard setup.py and requirements.txt.

The only other thing that most projects will need is a run.py.

### The run.py

Since Pop-Build creates a single binary, it needs a single entry point. This entry point is defined in the file run.py. This is just a simple python script that is used to start your application. The contents of the run.py is typically the same code that is used in your setuptools entry point, or the startup script used in distutils. There is nothing special about the run.py, pop-build just needs an entry point that is clean python.

A typical run.py will look like this:

import myapp

def main():
myapp.start()

main()

Just some good old python! If you are building a pop project then pop-seed will create the run.py for you.

### Run Pop-Build

Thats right! All you need outside of a run.py your python project likely already has! Pop-Build uses the setup.py and requirements.txt files to build the environment used.

So assuming you have a standard python project defined, all you need to do is cd to that directory and run pop-build, in this example we will assume the application is called foo:

pop-build -n foo

This will kick off the process and the resulting binary will be placed in dist/foo

Now that the binary is available it can be directly called.

### What Happened?

Pop-Build starts with the version of python that you exceuted pop-build with. This python is the python that will be embeded in your binary. Next it creates a venv for your application. With the venv in hand, Pop-Build populates it. The venv is populated with all of the deps that are defined as requrements for the main application, including the application itself.

Now that the venv has been set up, we tell PyInstaller to create a binary from the run.py. But PyInstaller is all about building a binary from all of the imports that come from the run.py. This is done to build a small binary and include only the most required code. But this is not the case for many applications, it is typical that things are late imported and the application assumes that a larger python environment is available. It is also typical that extra files are needed by the application and are typically added via the setup.py.

Instead of following the imports, Pop-Build bundles the venv into the binary created by PyInstaller. This means that you have a strong assurance that the full, needed environment is available. This does make a larger binary, but it allows for a much easier and reliable build. Also, the binary is typically not much bigger.

Many python projects require C libraries. How is it then, that the dynamic libs can be added to the final binary? Pop-Build has an answer to this.

When running pop-build we can use a configuration file. This file allows for any option that would be passed on the cli to be defined, but also to define the routines for external builds.

A Pop-Build config, that as an example, adds the library libsodium looks like this:

build:
libsodium:
make:
- tar xvf LATEST.tar.gz
- cd libsodium-stable && ./configure && make
src: libsodium-stable/src/libsodium/.libs/libsodium.so
dest: lib/

This example shows how we can define a library to download and build, then the src which is relative to the root of the build and the dest which is relative to the root of the venv.

The src can be a directory or a list of files, the dest is just a single directory to store the files.

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