Python Development

Now What?

• More Python
• Making your programs for others
• Releasing your code
• Licensing
• Collaborating
• Testing / Building

Imports

• Imports should always be written at the top of the file, after any module comments and docstrings.

• Imports should be divided according to what is being imported. There are generally three groups:

  • standard library imports (Python’s built-in modules)
  • related third party imports (modules that are installed and do not belong to the current application)
  • local application imports (modules that belong to the current application)

• Each group of imports should be separated by a blank space.

• https://pep8.org/#imports

Naming Conventions

• Functions & Variables: lowercase with underscores

  • Ex: my_special_number, square_root

• Classes: Use CamelCase

  • Ex: MyClass, RigidBody, AddressBook

• Constants

  • GRAVITY=9.81

• https://pep8.org/#overriding-principle

Structuring your Python projects

• Classes* – Containers of data & functions

• Modules* – individual python files

• Packages* – like folders of files, often structured that way too

• Projects* – Multiple packages, documentation, examples, unit tests, and distribution code all put together

• • can be much more complicated than this

Classes

• Classes vs Class Instances
• Inheritance
  • Object class
• Instance Methods, Class Methods, Methods

Make a Class

Instance Methods & Class Methods

Modules

• Typical structure:
  • Import packages & modules
  • Define functions
  • Code which always gets run, on import or main
  • Test for main
    • Run local script

Packages

• Typically a folder with code grouped together
• /folder – this name is the name of the package
  • __init__.py – required to be a package
  • module1.py - submodules
  • module2.py
• If you want to load a package it should be in your python path.
• __init__.py gets run when you import a package. Can use this to pre-load submodules or define constants, etc.

Packages

• Any folder with an __init__.py file in it
• Must be somewhere in PYTHONPATH

Packages you already have

• spyder: Python GUI
• pyyaml: read/write yaml files (like json)
• numpy, scipy: arrays and linear algebra
• sympy: symbolic equations
• pyqt: GUI development
• pyopengl, pyqtgraph:
• matplotlib: plotting
• jupyter: web-based inline interactive coding
• shapely: 2D geometry engine
• pillow, lxml, pandoc, ezdxf, imageio, meshio,
• Pypoly2tri, idealab_tools, foldable_robotics, pynamics
• cython: c compiler for python

Other Packages

• OpenCV
• networkX
• sphinx
• tornado
• pycairo – graphics library for pdf, svg…
• gitpython – work with git
• pythonocc – CAD
• kivy – Android-compatible gui framework
• pyserial
• pygame

Python Path

• The list of directories python searches for your code in
  • Looks first in the folder you are running the script from
  • Secondarily, looks in all the places you have added in your $PYTHONPATH environment variable
  • Third, looks in Python system directories (many of them, different by os)
• This list can be viewed and edited in the sys module under the path variable

Projects

/Project  
  /documentation  
  /examples  
  /python  
    /package1
      __init__.py  
      /subpackage1  
        __init__.py  
    /package2  
      __init__.py  
  /licenses – where you put the licenses of the code you are reusing with permission  
  setup.py  
  LICENSE  
  README  

Example: foldable_robotics

Speeding up Python

• Python is interpreted, not compiled.
• How do you work with compiled code?
• Simplest way: load_dll
  • Requires that dll to be in your system path, machine dependent.
• Try cython.
  • Convert your python code into c
  • Compile your c code into a dll
    • doesn’t have to be from python originally
    • Now supports c++! (with some glue code)
    • Requires a compiler to be installed
  • Import the dll just like a normal python module
  • However, machine dependent.

Example: pypoly2tri

Making Windows and applications

• PyQt4 / PyQt5 / PySide – Qt
  • Many others, but this is very cross-platform, used a lot, etc
• Already have PyQt5 installed in your anaconda distribution
• Way to create windows, menus, etc
• Turn your script into a user application

Example: putting matplotlib in a window

• https://github.com/idealabasu/code_idealab_empty_project

Collaborative projects

• Git – versioning tool
  • Command-line tool for tracking and committing changes
  • many guis available
  • I suggest “git-extensions” for windows
• Github
  • website built around git: https://github.com/
  • Other collaboration tools
    • Documentation, bugtracking, code releases
  • Integration with other services

Concept of GIT

• Work simultaneously, merge your code when ready
• There is no central administration, repositories can be local or on the web
• Create branches to manage

Example

Licensing – really important

• Strongly encourage you to learn about licensing. The future of your work depends on it.
• Copyright and who owns it.
• “What is Open source?”
  • Ability to see/use/change/release others’ code?
  • Ability to use others’ code with your code
• Copyright vs copyleft
  • GPL, LGPL, MIT, BSD, Apache

Distributing your Code

• setup.py
• Make a pip project and deploying to Pypi
  • https://packaging.python.org/tutorials/packaging-projects/
• Freezing your code
  • Py2exe,pyinstaller, cx_freeze,
• Creating an Anaconda package

Setup script

• This is the basic way to release and install python code.
• Installing moves project code from local folder to python system directory.
• Download source, open command terminal, type
  • “python setup.py install”
  • Can also build, build_ext, etc.
• Being phased out in favor of pip
• Setup script still important

Future

• This class
  • One of a kind
  • Still emerging
  • Chance to define it
• Research
  • Open field
  • Can move faster
  • New manufacturing processes need new design tools

Wrapup

• You’ve built many parts you find in CAD
  • Motion analysis – nonlinear constraint solving – how sketches are dimensioned, how assemblies are moved around.
  • Python code for
  • Constructive Solid Geometry
    • Union, difference, intersection
  • Manufacturing
    • Accessing the functions for understanding the manufacturing process
  • Dynamics? Some
  • Stiffness? Some
  • Kinematics? Some