Python Notes

General

Naming conventions

• Naming conventions of Python from PEP 8

How functions work

• How to use *args and **kwargs in Python
• 函數有無返回值？
• Re: 函數有無返回值？

Precedence

• Operator precedence
• Boolean operations - and, or, not for short-circuit operators.

Getting help

• help. For instance, help(len), or help(tuple.index) for known functions or methods.
• In IPython (e.g. Jupyter Notebook), ? len also works.

Python standard library

While The Python Language Reference describes the exact syntax and semantics of the Python language, this library reference manual describes the standard library that is distributed with Python. It also describes some of the optional components that are commonly included in Python distributions.

• venv provides a convinient way to creat "lightweight 'virtual environments'". Read Virtual Environments and Packages for the official tutorial.

Built-in functions

• dir returns all methods (attributes) of specified instance (object).
• type returns the data type of the object in Python.
• import is like source and library in R, sourcing packages or script files.
• len returns the length of the object. (cf: length in R)
• set returns unique values in the object, and that allows mathematical set operations. list(set(a_list)) is a way to have unique values in the list a_list. (cf: unique in R; pandas.Series.unique in pandas library)
• zip returns a mapped iterable from multiple instances (objects).
• enumerate returns an enumerate object. It is useful with itemgetter in operator module when finding maximum value and its index in a list.

Assigning values

• =. a = b means that a is b is True and they share the same memory, i.e. changing a will change b. (cf: a = b or a <- b in R copies b and assigns that to a, i.e. changing a won't change b. Read also Use "<-" or "=".)

Comparison

• My Gist comparison.py demonstrates the difference between == and is. Besides I mention pd.DataFrame.equals there for comparing DataFrames.

Functions for programming

Unlike R, Python is usually not a functional programming language. Still, these following functionalities provide essential help or comparison.

• lambda are Python's way of creating anonymous functions. This is unlike R.

  You declare a lambda function with the word lambda followed by a list of arguments, followed by a colon and then a single expression and this is key. There's only one expression to be evaluated in a lambda. The expression value is returned on execution of the lambda.

• map is kind of like sapply in R. See defining functions in R and Python for an example.

Useful packages (ordered alphabetically)

• fancyimpute

  A variety of matrix completion and imputation algorithms implemented in Python including MICE and k-NN.

• NumPy

  NumPy is the fundamental package for scientific computing with Python.

• pandas

  pandas is an open source, BSD-licensed library providing high-performance, easy-to-use data structures and data analysis tools for the Python programming language.

  • See Comparison with R / R libraries for reference to equivalent functionality in R.
  • How to deal with non-decodable bytes with importing data with pandas (written in Mandarin)
  • Check my asked questions about pandas on Stack Overflow.

• pipenv

  Python dev workflow for humans

• pipreqs

  Generate requirements.txt file for any project based on imports

• regex

  This regex implementation is backwards-compatible with the standard 're' module, but offers additional functionality.

Engineering tools using Python

• docker

  • A scalable, VM-like solution
  • Official getting started
  • Python docker hub for getting Python environment in docker
  • Personal notes of docker

• gRPC

  • Build protocol for backend services (What is gRPC?)
  • Official documents by languages
  • Proto3 language guide
  • gRPC/Python docker hub for building gRPC services in Python in docker environment
  • gRPC GitHub
  • Comparing gRPC with REST
    • REST vs. gRPC: Battle of the APIs
    • How gRPC is convinced to be chose over REST
    • How is gRPC different from REST?
  • References in practice
    • How to get top-level protobuf enum value name by number in python?
    • Handing errors in gRPC
      • gRPC errors - A handy guide to gRPC errors
      • Raising a server error to the client with gRPC
      • Status codes and their use in gRPC