Python Tutorial - 2
4.Loops
4.1 For Loop
4.2 Range
4.3 While loop
4.4 Break loop
4.5 Nested loop
4.6 List Comprehension
4.1 For Loop
4.2 Range
4.3 While loop
4.4 Break loop
4.5 Nested loop
4.6 List Comprehension
5.Functions
5.1 Built-In Functions
5.2 Functions
5.3 Lambda Expressions
5.4 Map
5.5 Filter
5.1 Built-In Functions
5.2 Functions
5.3 Lambda Expressions
5.4 Map
5.5 Filter
4.Loops
A loop statement allows us to execute a statement or group of statements multiple times.
4.1 For Loop
# For loops are used for iterating over a sequence (a list, a tuple, a dictionary, a set, or a string).
# An action can be executed once for each item in a list, tuple of the for loop.
my_list = [1, 2, 3]
my_list
for i in my_list:
print(i)
# you can do more than one task for every loop such as printing out 'Hello world'
for i in my_list:
print(i)
print('Hello World')
Hello World
2
Hello World
3
Hello World
# List of strings
my_list = ['AAPL', 'GOOG', 'T', 'TSLA', 'SP500']
for i in my_list:
print(i)
GOOG
T
TSLA
SP500
# you can loop over a string as follows
for i in 'TSLA':
print(i)
S
L
A
Write a code that takes in a string and prints it out on the screen except for any letter 'T'. You can replace the letter 'T' with '*'.
for letter in 'TUSHAR':
if letter == 'T':
print('*')
else:
print(letter)
U
S
H
A
R
4.2 Range
# Range() generates a list of numbers, which is used to iterate over with for loops.
# range() is 0-index based, meaning list indexes start at 0, not 1.
# The last integer generated by range() is up to, but not including, last element.
# Example: range(0, 10) generates integers from 0 up to, but not including, 10.
for i in range(6):
print(i)
1
2
3
4
5
# Range of numbers from 1 to 20 with steps of 2
for i in range(1, 20, 2):
print(i)
3
5
7
9
11
13
15
17
19
for i in reversed(range(5)): print(i)
3
2
1
0
Write a code that takes in the maximum and minimum limits from the user and prints out even numbers only between the provided range
min = int(input("Enter the price (lower bound: "))
max = int(input("Enter the price (Upper bound: "))
for i in range(min, max):
if i%2 == 0:
print(i)
Enter the price (Upper bound: 6
2
4
Write a code that generates the following table:
1 1 1 2 4 8 3 9 27 4 16 64 5 25 125 6 36 216 7 49 343 8 64 512 9 81 729 10 100 1000
for x in range(1, 11):
print('{} {} {}'.format(x, x*x, x*x*x))
2 4 8
3 9 27
4 16 64
5 25 125
6 36 216
7 49 343
8 64 512
9 81 729
10 100 1000
4.3 While Loop
# While loop can be used to execute a set of statements as long as a certain condition holds true.
i = 0
while i <= 15:
print(i)
i = i + 1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Write a code that displays numbers from 1 to 30 (including 30) using for and while loops
i = 1 while (i < 10): print (i) i = i+1
2
3
4
5
6
7
8
9
for i in range(1, 6):
print(i)
2
3
4
5
Create a rolling dice game that assume we have two dice (#1 and #2). The dice is being thrown and a random number is generated everytime. The game should be designed such that it prompts the user to ask if he/she would like to keep playing or exit the game.
import random
keep_rolling = "y"
while keep_rolling == "y":
print("Rolling the dices, please wait!...")
print("Rolling results for Dice #1:", random.randint(1, 6))
print("Rolling results for Dice #2:", random.randint(1, 6))
keep_rolling = input("Do you want to roll again?")
Rolling results for Dice #1: 2
Rolling results for Dice #2: 3
Do you want to roll again?y
Rolling the dices, please wait!...
Rolling results for Dice #1: 3
Rolling results for Dice #2: 3
Do you want to roll again?n
4.4 Break a Loop
# break() is used to exit a for loop or a while loop
# continue() is used to skip the current block, and return to the "for" or "while" statement.
my_list = ["GOOG", "AAPL", "T", "TSLA", "SP500"]
my_list
# print out all elements in the list
for i in my_list:
print(i)
AAPL
T
TSLA
SP500
# print out all elements in the list up until the AT and T stock (Ticker Symbol = T) is detected
for i in my_list:
print(i)
if i == 'T':
break
AAPL
T
# Print only odd elements and skip even numbers
my_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for i in my_list:
if i%2 == 0:
continue
print(i)
3
5
7
9
Write a code that continiously gets data from the user and calculates the average and print out on the screen. The code exits when the user enters 'e'.
print("Keep entering numbers and
I will display the average to you!")
avg = 0
n = 0
while True:
x = input("Enter a number: ")
# Check if the user wants to exit (i.e.: break the loop)
if x == 'e':
break
x = int(x)
n = n + 1
avg = ((avg * (n - 1) ) + x) / n
print ("The current average is ", avg)
Keep entering numbers and
I will display the average to you!
Enter a number: 2
The current average is 2.0
Enter a number: 3
The current average is 2.5
Enter a number: e
4.5 Nested Loop
# Nested loops are loops that exist inside the body of another loop
for x in range(1, 3): # slow loop
for y in range(1, 11): # fast loop
print('{} * {} = {}'.format(x, y, x*y))
1 * 2 = 2
1 * 3 = 3
1 * 4 = 4
1 * 5 = 5
1 * 6 = 6
1 * 7 = 7
1 * 8 = 8
1 * 9 = 9
1 * 10 = 10
2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20
color_list = ['black', 'white', 'gold']
phone_list = ['iphone', 'samsung', 'blackberry']
for i in color_list:
for j in phone_list:
print(i, j)
black samsung
black blackberry
white iphone
white samsung
white blackberry
gold iphone
gold samsung
gold blackberry
Write a code that takes in a number (range between 1 and 9) from the user and print out the multiplication table up until that number.
number = int(input("Enter a number between 1 and 9: "))
for x in range(1, number+1): # slow loop
for y in range(1, 11): # fast loop
print('{} x {} = {}'.format(x, y, x*y))
Enter a number between 1 and 9: 1
1 x 1 = 1
1 x 2 = 2
1 x 3 = 3
1 x 4 = 4
1 x 5 = 5
1 x 6 = 6
1 x 7 = 7
1 x 8 = 8
1 x 9 = 9
1 x 10 = 10
4.6 List Comprehension
# List comprehension is an elegant tool to transform one list into another list.
# Instead of using loops and append, list comprehension is used to iterate over a list, condition its elements and include them in a new list.
# Let's take a look at the traditional way of taking a list and squaring its elements
input_list = [1, 2, 3, 4]
output_list = []
for element in input_list:
output_list.append(element **2)
print(output_list)
# List comprehension is a super powerful one line of code!
[ element ** 2 for element in input_list]
# Let's square even numbers only
# We need to insert a condition
input_list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
output_list = []
for i in input_list:
if i % 2==0:
output_list.append(i**2)
print(output_list)
# All this could be done with one line of code as well using List Comprehension
output_list = [i**2 for i in input_list if i%2 == 0 ]
output_list
# All this could be done with one line of code as well using List Comprehension
output_list = [i**2 for i in input_list if i%2 == 0 ]
output_list
Write a code that takes in a list of prices of a stock for the past 7 days and then normalize the prices
print('Enter a list of past 7-days prices separated by a space:')
prices = [int(x) for x in input().split()]
70 50 80 70 80 30 20
normalized_prices = [ (i/prices[0]) for i in prices]
print('Orginal Prices: {}\nNormalized Prices: {}\n'.format(prices, normalized_prices))
Normalized Prices: [1.0, 0.7142857142857143, 1.1428571428571428, 1.0, 1.1428571428571428, 0.42857142857142855, 0.2857142857142857]
5. FUNCTIONS
A function is a block of code which only runs when it is called.
5.1 Built-In Functions
# There are many built-in functions that you can leverage directly
# Let's define 2 lists x and y
x = [4, 5, 1, 2, 8, 5]
y = list(range(1, 7))
x
y
# Let's obtain the length of y
len(y)
# Let's obtain the minimum value
min(x)
# Let's obtain the maximum value
max(x)
# Let's create a tuple out of the list
z = tuple(x)
z
type(z)
# Let's obtain the sum of elements in x
print(sum(x))
Write a code that takes in 2 lists x = [-1 -4 -7] and y = [-3 7 4] and calculates the absolute sum of all its elements |x+y|
x = [-1, -4, -7]
y = [-3, 7, 4]
z = abs(sum(x+y))
z
5.2 Functions
# Let's define a function named "my_function" that does not receive any arguments
# The function simply prints out content and does not return anything
def my_function():
print('Welcome to Python course!')
# Function call
my_function()
# Define a function that takes in argument x and return the squared value
def squared(x):
return x ** 2
# Call the function
output = squared(4)
output
# Define a function with default value
def my_function(amount = 20000):
print("My total amount is = {}".format(amount))
# If you pass an argument to the function, it overwrites the default value
my_function(600000)
# If you don't pass an argument, the default value "20000" will be used instead
my_function()
Write a code that takes in two inputs (number of units and prices) from the user and calculate the total account balance
def total(units, price):
amount = units * price
return(amount)
num_unit = int(input("Enter the number of unit: "))
price = int(input("Enter the price per unit: "))
account_balance = total(num_unit, price)
print('Total account balance = {}'.format(account_balance))
Enter the number of unit: 5
Enter the price per unit: 50
Total account balance = 250
5.3 LAMBDA EXPRESSIONS
# Lambda function is used to create a function without a name
# Lambda functions are mainly used with filter() and map() [they will be discussed later on].
# Lambda function can receive any number of arguments, but can only have one expression.
# let's see how to create a basic function that squares the input
def my_function(x):
return x**2
# Function callmy_function(3)
# We can do the same task using Lambda expression
# Note that there is no function name
y = lambda x:x**2
y(3)
# Note that lambda expression can take in more than one argument
# there is only one expression that could be performed
def summation(x, y, z):
return x+y+z
result = summation(1, 2, 3)
result
result = lambda x, y, z : x+y+z
result(1, 2, 3)
Write a code that takes in two inputs from the user and calculates the total using lambda expressions instead
num_unit = int(input("Enter the number of unit: "))
price = int(input("Enter the price per unit: "))
account_balance = lambda num_unit, price : num_unit * price
print('Total = {}'.format(account_balance(num_unit, price)))
Enter the price per unit: 50
Total = 250
4. MAP
# The map() function takes in a function and a list.
# map() performs an operation on the entire list and return the results in a new list.
# Define two lists a and b
a = [1, 4, 5, 6, 9]
b = [1, 7, 9, 12, 7]
# Let's define a function that adds two elements together
def summation(a, b):
return a + b
# You can now use map() to apply a function to the entire list and generate a new list
c = list(map(summation, a, b))
c
# map could be used with Lambda as follows
# lambda function is an anonymous function that take any number of arguments and can only have one expression
input_list = [1, 2, 3, 4]
out_list = list(map ( lambda x:x**2 , input_list))
out_list
MINI CHALLENGE #4 SOLUTION: Write a function that takes an argument and return its cubic value Define a list of integers ranging from -10 to 10 Apply the function to the entire list and generate a new output list
def cubic(x):
return (x*x*x)
numbers = range(-10, 11)
numbers_cubed = list(map(lambda x: cubic(x), numbers))
print(list(numbers))
print(numbers_cubed)
[-1000, -729, -512, -343, -216, -125, -64, -27, -8, -1, 0, 1, 8, 27, 64, 125, 216, 343, 512, 729, 1000]
5.5 FILTER
# filter is used to create a list of elements for which a function returns "True".
prices = [105, 5055, 40, 356, 923, 1443, 222, 62]
# return only even numbers
out = list(filter( lambda x: (x % 2 == 0) , prices ))
out
# Return prices that are greater than or equal 100
prices = [105, 5055, 40, 356, 923, 1443, 222, 62]
out = list( filter(lambda x: (x>=100) , prices) )
out
# Return values between 200 and 250
out = list( filter(lambda x: (x>=200 and x<=250) , prices) )
out
# Return values between 200 and 250
out = list( filter(lambda x: (x>=200 and x<=250) , prices) )
out
Write a code from the user that takes in a range (upper and lower bounds) and returns a list of positive and even numbers only
min = int(input("Enter a number (lower bound) *must be negative* : "))
max = int(input("Enter a number (Upper bound:) "))
numbers = range(min, max)
even_greater_than_zero = list(filter(lambda x: (x > 0 and x%2 == 0), numbers))
print(even_greater_than_zero)
Enter a number (Upper bound:) 5
[2, 4]
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