Basics of Python

Bhavika Tekwani

btekwani@gmu.edu

slides.com/bhavika/python

Overview

Introduction
Data types
Data structures
Control flow statements

Why Python?

Dynamic & readable
General purpose: there's nothing Python can't do
Community support: libraries, documentation, online support (StackOverflow, IRC, etc)
Good "first language" to begin programming in

Logistics

Python 3.6
Anaconda for Windows - a Python distribution that bundles the installation of several libraries
Spyder IDE

Syntax

print ("Hello World")

print ("

Try this out. Print your own name.

s1 = "Hello World"

s2 = "The quick brown fox jumped over the lazy dog"

s3 = "Oh no, what has he done today?!"

print (s1)

print (s1 + s2)


name = "Bhavika Tekwani"

print (name.split(' '))

Strings

Integers

# Try adding two integers

x = 3
y = 10

sum = x + y

print (sum)

# Another example: 

a = 23
b = 67

print (a+b)

Float

x = 3.0

y = 4.5

print (x+y) 

Now try,

x = 3
y = 4.5


a = 6.0009000090
b = 2.1

print (a+b)

Data Structures

Used to group and organize data together
Usually for similar or related data
Makes processing data easier

Lists



# This is what a list looks like:

x_list = []


y_list = [1, 2, 3, 4]

# You can combine two lists:

print(x_list + y_list)



# You can add elements to a list:

x_list.append(3)


# Remove an element from a list:

y_list.remove(4)


# What happens if you do the following? 

y_list.remove(100)


# position, value to be inserted

x_list.insert(4, 6)

# Count the occurrence of an element in the list
x_list.count(4)

# Sort a list
x_list.sort()

# Let's work with some data
# Addresses: Street, City, ZIP code

address1 = ['4400 University Drive', 'Fairfax', 22031]
address2 = ['9490 Blake Ln', 'Fairfax' , 22031]
address3 = ['9110 Lee Hwy', 'Fairfax', 22030]

address_data.append(address1)
address_data.append(address2)
address_data.append(address3)

print (address_data)

Dictionaries


# This is how you define a dictionary

bank_account = {'jack': 1, 'john': 2, 'michelle': 3}

print (bank_account['jack'])

print (bank_account['jane'])


# Add a key-value pair

bank_account['jane'] = 4


# Check if a given key-value pair exists

print ('jane' in bank_account)


# Check what the dictionary has

k = list(bank_account.keys())

print (k)

Sets

# Defined as: 

lakers = {'ingram', 'russell', 'black', 'robinson'}

print (lakers)

a = set('abcdefg')
print (a)

b = set('acdf')
print (b)

# letters in a but not b
print (a-b)

# letters in a and b both
print (a&b)

# letters in either a or b
print (a | b)

# letters in a or b but not both
print (a^b)

Control Flow Statements

if...else
for loop
break, continue
while
with

...and a few others

if...else statement


# read a number from the user

n = int(input("Please enter an integer"))

if n < 0:
    print ("You entered a negative number")

elif n == 0:
    print ("You entered zero")

else:
    print ("You entered: ", n)

for loop

# Let's iterate over a list 


pets = ['cats', 'dogs', 'guinea pigs', 'lizards']

for p in pets:
    print (p, len(p))



# Print a lot of numbers
# Try changing the range

for i in range(10):
    print (i)

 

# Range with a start and end

for i in range(5, 9):
    print (i)

while loop



# While some condition is true, do something

count = 0 

while (count < 9):
    print ("Current count:", count)
    count = count + 1;



# Use else with while


count = 0

while count < 10:
    print ("Count is ", count)
else:
    print ("Count has exceeded 10")

break & continue



# break statement

n = 0

for n in range(9):
    n = n + 1

    if (n == 5):
        break;


    print ("n :", n)

print ("Outside the for loop")


# continue statement

n = 0

for n in range(9):
    n = n + 1


    if (n == 7)
        continue;

    print ("n : ", n)

Functions

Units of code that achieve specific goals
Can accept input and offer output
Usually small, self-contained pieces of logic


# function definition

def hello():
    print ("Hello World!")

# function call
hello()



# let's give a function some input


def add(a, b):
    print (a+b)

add(3, 5)


# let's get some output from a function


def square_number(n):
    return n*n

sq = square_number(10)

print (sq)