Python Programming

Basic concepts

Data structure

Variable

• Number
• String
• Tuple
• List: Mutable, container
• Dictionary: Mutable, container
• Set: Mutable, container
• None: empty value

tuple = (1, 2, 3)
list = [1, 2, 3]
dict = {"ele1":1, "ele2":2, "ele3":3}

Operators

Numerical Operators: - < : less than - > : greater than - <= : less than or equal to - >= : greater than or equal to - == : equal to - != : not equal to

String Operators: - == : equal to - != : not equal to

Logical Operators: - and - or - not

Conditional execution

Conditional execution in Python is achieved using the if/else construct (if and else are reserved words).

# Conidtional execution
x = 10
if x > 10:
    print("I am a big number")
else:
    print("I am a small number")

# Multi-way if/else
x = 10
if x > 10:
    print("I am a big number")
elif x > 5:
    print("I am kind of small")
else:
    print("I am really number")

Iteration/Lopps

Two looping constructs in Python

• For : used when the number of possible iterations (repetitions) are known in advance

• While: used when the number of possible iterations (repetitions) can not be defined in advance. Can lead to infinite loops, if conditions are not handled properly

for customer in [“John”, “Mary”, “Jane”]:
    print(“Hello ”, customer)
    print(“Please pay”)
    collectCash()
    giveGoods()

hour_of_day = 9
while hour_of_day < 17:
    moveToWarehouse()
    locateGoods()
    moveGoodsToShip()
    hour_of_day = getCurrentTime()

What happens if you need to stop early? We use the break keyword to do this.

It stops the iteration immediately and moves on to the statement that follows the looping

while hour_of_day < 17:
    if shipIsFull() == True:
        break
    moveToWarehouse()
    locateGoods()
    moveGoodsToShip()
    hour_of_day = getCurrentTime()
collectPay()

What happens when you want to just skip the rest of the steps? We can use the continue keyword for this.

It skips the rest of the steps but moves on to the next iteration.

for customer in ["John", "Mary", "Jane"]:
    print(“Hello ”, customer)
    print(“Please pay”)
    paid = collectCash()
    if paid == false:
        continue
    giveGoods()

Exceptions

• Exceptions are errors that are found during execution of the Python program.
• They typically cause the program to fail.
• However we can handle them using the ‘try/except’ construct.

num = input("Please enter a number: ")
try:
    num = int(num)
    print("number squared is " + str(num**2))
except:
    print("You did not enter a valid number")

General functions

help()
type()
len() 
range()
list()      
tuple()
dict()

Reference

• https://www.py4e.com/
• https://omgenomics.com/
• https://www.coursera.org/learn/bioinformatics
• http://do1.dr-chuck.com/pythonlearn/EN_us/pythonlearn.pdf
• https://www.py4e.com/html3
• http://do1.dr-chuck.com/pythonlearn/EN_us/pythonlearn.epub
• Primer on Python for R Users