Python is undoubtedly one of the most popular computer programming languages in today’s world. I learned about it before and during my MDS program. This post is to summarize some fundamentals of Python programming.

Data types

Python has data types listed in below table:

Notes:
1. strings, tuples and ranges are immutable types. lists are mutable.
2. The major difference between lists and tuples is that a list is used as a homogeneous sequence, but a tuple is used as a heterogeneous sequence.

Each data type has some methods. Take string data type as an example:

• str_greeting = “How are you?”
• str_greeting.split()
• str_greeting.lower()
• len(str_greeting)

Take list as another example:

• age_list = [18, 19, 20, 18]
• age_list.append(22)
• age_list.count(18)
• len(age_list)
• type(age_list)
• age_list[0]
• age_list[0:2]

Here is a list of commonly used built-in functions:

• print(x)
• type(x)
• range(a, b, n)
• len(seq)
• abs(x)
• sum(seq)
• max(seq)
• min(seq)
• sorted(seq)
• list(seq)

Operators

Python has below arithmetic operators:

• + # plus
• - # minus
• * # multiply
• / # divide
• ** # 幂/次方，exponentiation
• // # 取整，integer division
• % # 取余

Python has below comparison operators:

• x == y
• x != y
• x > y
• x >= y
• x < y
• x <= y

Control Flow

The most common types of control flow:

• if-elif-else
• while
• for

Functions

This is how to define functions in Python:

def square(n):
  square = n**2
  return(square)

Docstrings

A Docstrings is a string that follows immediately the def statement. It can be viewed using ? in Jupyter Notebook.

def square(n):
  "Compute the square of n."  
  square = n**2
  return(square)

Python Testing

Best practices: writing tests before you write code!!!

assert square(8) == 64, "The output of square(8) should be 64."  
print("Test passed. Success!")

Python class

class people():  
  def __init__(self, first_name, last_name):  
    self.first_name = first_name
    self.last_name = last_name  

  def __repr__(self):
    return '{} {}'.format(self.first_name, self.last_name)

  def greeting(self):
    print("Hello! My name is {} {}. Very nice to meet you!".format(self.first_name, self.last_name))

Python Modules and Packages

A Python module is a text file containing Python code that has a .py extension.

import samples      # import the module to current environment
type(samples)       # check the data type of 'samples'
dir(samples )       # list all the methods and attributes in 'samples'  

A Python Package is a collection of Python modules. We can think of Python modules as files and Python packages as directories. We can use import to import a package.