CS110_Lesson5_Notes.py

Python3 Editor

#     LOOPS
#-----------------------------------------

# Loops are used to repeat a set of statements.

# In python, there are for-loops and while loops. A for-loop runs a specific number of times.
# It's syntax is always written like this:

# for i in some_list:
#     some code

# i = the iterating variable, it can be named anything so long as it's not a variable already in use
# some_list = a list of values for it to iterate through

# the range() function generates a range() object. There are 3 ways to use it:
# range(end) = generates a range object containing values starting at 0 and ending at end-1.
print("range(10) =", list(range(10)))

# range(start, end) = generates a range object containing values starting at start, ending at end-1. 
print("range(5, 12) =", list(range(5, 12)))

# range(start, end, skip) = generates a range object containing values starting at start, ending at end-1, and skipping by the skip value
print("range(2, 20, 2) =", list(range(2, 20, 2)))
print()

# The following loop will iterate through the range(10) object, which contains [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].
# The first time it runs, i = 0 (first item in list), so it prints out '0'.
# Second time it runs, i = 1 (second item in list), so it prints out '1'.
# This continues until it reaches the last item in the list, prints it out, and stops running the loop.
for i in range(10):
    print(i, end=" ")
    
print()
    
# You can assume that the loop iterating variable is storing the current value in the iteration, so you can do operations to it,
# depending on its type. When using range(), the iterating variable's type is an integer.
for i in range(10):
    print(i**2, end=" ")
print('\n')

# Let's say you already have a list of items, you can use a loop to iterate through those as well.
# In the example below, it will calculate the average of a list of grades. Since each grade is a float, the iterating variable
# will also be storing a float (instead of an integer)
grades = [95.4, 77.6, 54.2, 67.9, 83.0]
total = 0
for g in grades:
    print(g, end=', ')
    total += g
print()
avg = total/len(grades)
print('The total is', total)
print('The average is', avg)
print()

# Remember that a string is like a list of characters? You can use a for-loop to iterate through EACH character in a string.
s = "Dinosaur"
for c in s:
    print(c, end=" ")
print("\n")

# You can also check conditions inside the for-loop, and can check properties of each character in the string.
s = 'Dino1 saur!'
for c in s:
    if c.isalpha():
        print(c, "is a letter!")
    elif c.isdigit():
        print(c, "is a digit!")
    elif c.isspace():
        print(c, "is a space!")
    elif c in ['!', '@', '#', '$', '%', '^', '&']:
        print(c, "is a character!")
    else:
        print(c)
print()

#------------------------------------------------------
#    Break, Continue
#------------------------------------------------------

# If you are iterating (looping) through something and checking for a specific condition, 
# you can stop the loop when that condition is true by using the keyword 'break'

# The example below will print out 0 1 2 3 4 5 6 and will stop running the loop, when i == 7.
for i in range(10):
    if i == 7:
        break
    print(i, end=' ')
print()

# If you want to skip a specific iteration, you can use the keyword 'continue'
# The example below will print out 0 1 2 3 5 6 8 9. Notice that 4 and 7 are missing?
# It will hit the 'continue' keyword, ignore the rest of the code in the loop, and 
# return back to the loop header to go to the next iteration.
for i in range(10):
    if i == 4 or i == 7:
        continue
    print(i, end=' ')
print('\n')

#---------------------------------------------------------------------------------
#        While loops
#---------------------------------------------------------------------------------

# While loops are used when you want to run a loop until a certain condition is true, 
# but it may not need to run an exact number of times. 
# The format for a while loop is:
# while condition:
#     some code

# Example: Asking the player to enter input over and over again until it's valid.
# If they enter a valid choice the first time, the loop won't run. But each time they enter something invalid,
# the loop will run and ask them to try again.
choices = ['rock', 'paper', 'scissors']
player = input("Enter a choice " + str(choices) + ": ").lower()
while player not in choices:
    print("Invalid input:", player)
    player = input("Enter a choice " + str(choices) + ": ").lower()
print("Final choice:", player)
    
# Example: Run until they guess the right value
guess = input("Guess a letter: ").lower()
correct = 'h'
while guess != correct:
    print("Wrong!")
    guess = input("Guess a letter: ").lower()
print("CORRECT! The letter was", correct)
print()

# You can also use this to run similar to a for-loop, but you don't need the iteration to always increase the iterating variable.
i = 0
while i < 8:
    if i % 2 == 0:
        print(i, "is even so", end=" ")
        i += 3
    else:
        print(i, "is odd so", end=" ")
        i -= 1
    print("i =", i)
print()

( around 117 lines Python3 code )

Published By:

Mentor Sabrina

Created on 2020-11-09T13:54:03Z

Python3 Editor - an OYOclass application, own your own class today.

Result

Status: Program is not running