Computer Science in Python

Computer science is no more about computers than astronomy is about telescopes, biology is about microscopes or chemistry is about beakers and test tubes. Science is not about tools, it is about how we use them and what we find out when we do. (Michael Fellows and Ian Parberry, “SIGACT trying to get children excited about CS”)

Preface

Python functions are defined using def keywords:

def sign(x):
    if x > 0:
        return 'positive'
    elif x < 0:
        return 'negative'
    else:
        return 'zero'

for x in [-1, 0, 1]:
    print sign(x)
# Prints "negative", "zero", "positive"

def hello(name, loud=False):
    if loud:
        print 'HELLO, %s!' % name.upper()
    else:
        print 'Hello, %s' % name

hello('Bob') # Prints "Hello, Bob"
hello('Fred', loud=True)  # Prints "HELLO, FRED!"

Variables

Data Types

Strings

txt = "I love apples, apple are my favorite fruit"
x = txt.count("apple")
print(x)

myDict = {"name": "John", "country": "Norway"}
mySeparator = "TEST"
x = mySeparator.join(myDict)
print(x)

# Python code to demonstrate working of 
# strip(), lstrip() and rstrip() 
str = "---python3---"

# using strip() to delete all '-' 
print ( " String after stripping all '-' is : ", end="") 
print ( str.strip('-') ) 

# using lstrip() to delete all trailing '-' 
print ( " String before stripping all leading '-' is : ", end="") 
print ( str.lstrip('-') ) 

# using rstrip() to delete all leading '-' 
print ( " String after stripping all trailing '-' is : ", end="") 
print ( str.rstrip('-') )

Numbers

Boolean

Exception handling

Data Members

class Person:
  # data members
  salary = 23 
  def __init__(self, name, age):
    Person.name = name
    self.age = age
    Person.salary += 1

  def __str__(self):
    return f"{self.name}({self.age})" + str(Person.salary)    

p1 = Person("John", 36)

print(p1)

Class

We can easily create the classes using class keyword in the following manner:

class Greeter(object):
    
    # Constructor
    def __init__(self, name):
        self.name = name  # Create an instance variable
        
    # Instance method
    def greet(self, loud=False):
        if loud:
            print 'HELLO, %s!' % self.name.upper()
        else:
            print 'Hello, %s' % self.name
        
g = Greeter('Fred')  # Construct an instance of the Greeter class
g.greet()            # Call an instance method; prints "Hello, Fred"
g.greet(loud=True)   # Call an instance method; prints "HELLO, FRED!"