In this part of my Learn to Program tutorial I will continue teaching how to program through solving programming problems. We will cover Exception Handling, Do While Loops, the Math Module, the Decimal Module, Strings, and a whole lot more.

If you missed the first part watch it first or you may be confused. All of the code follows the video below. The goal is to learn how common problems are solved so don’t worry if you get them wrong.

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Code & Transcript

# ---------- FORCE USER TO ENTER A NUMBER ----------
# By giving the while a value of True it will cycle until a break is reached
while True:

    # If we expect an error can occur surround potential error with try
    try:
        number = int(input("Please enter a number : "))
        break

    # The code in the except block provides an error message to set things right
    # We can either target a specific error like ValueError
    except ValueError:
        print("You didn't enter a number")

    # We can target all other errors with a default
    except:
        print("An unknown error occurred")

print("Thank you for entering a number")

# ---------- Problem : Implement a Do While Loop ----------
# Now I want you to implement a Do While loop in Python
# They always execute all of the code at least once and at
# the end check if a condition is true that would warrant
# running the code again. They have this format
# do {
#   ... Bunch of code ...
# } while(condition)

# I'll create a guessing game in which the user must chose
# a number between 1 and 10 of the following format
'''
Guess a number between 1 and 10 : 1
Guess a number between 1 and 10 : 3
Guess a number between 1 and 10 : 5
Guess a number between 1 and 10 : 7
You guessed it
'''

# Hint : You'll need a while and break

secret_number = 7

while True:
    guess = int(input("Guess a number between 1 and 10 : "))

    if guess == secret_number:
        print("You guessed it")
        break

# ---------- MATH MODULE ----------
# Python provides many functions with its Math module
import math

# Because you used import you access methods by referencing the module
print("ceil(4.4) = ", math.ceil(4.4))
print("floor(4.4) = ", math.floor(4.4))
print("fabs(-4.4) = ", math.fabs(-4.4))

# Factorial = 1 * 2 * 3 * 4
print("factorial(4) = ", math.factorial(4))

# Return remainder of division
print("fmod(5,4) = ", math.fmod(5,4))

# Receive a float and return an int
print("trunc(4.2) = ", math.trunc(4.2))

# Return x^y
print("pow(2,2) = ", math.pow(2,2))

# Return the square root
print("sqrt(4) = ", math.sqrt(4))

# Special values
print("math.e = ", math.e)
print("math.pi = ", math.pi)

# Return e^x
print("exp(4) = ", math.factorial(4))

# Return the natural logarithm e * e * e ~= 20 so log(20) tells
# you that e^3 ~= 20
print("log(20) = ", math.log(20))

# You can define the base and 10^3 = 1000
print("log(1000,10) = ", math.log(1000,10))

# You can also use base 10 like this
print("log10(1000) = ", math.log10(1000))

# We have the following trig functions
# sin, cos, tan, asin, acos, atan, atan2, asinh, acosh,
# atanh, sinh, cosh, tanh

# Convert radians to degrees and vice versa
print("degrees(1.5708) = ", math.degrees(1.5708))
print("radians(90) = ", math.radians(90))

# ---------- ACCURATE FLOATING POINT CALCULATIONS ----------

# The decimal module provides for more accurate floating point calculations
# With from you can reference methods without the need to reference the module
# like we had to do with math above
# We create an alias being D here to avoid conflicts with methods with
# the same name
from decimal import Decimal as D

sum = D(0)
sum += D("0.01")
sum += D("0.01")
sum += D("0.01")
sum -= D("0.03")

print("Sum = ", sum)

# ---------- STRINGS ----------
# Text is stored using the string data type
# You can use type to see the data type of a value
print(type(3))
print(type(3.14))

# Single quotes or double are both used for strings
print(type("3"))
print(type('3'))

samp_string = "This is a very important string"

# Each character is stored in a series of boxes labeled with index numbers
# You can get a character by referencing an index
print(samp_string[0])

# Get the last character
print(samp_string[-1])

# Get the last character
print(samp_string[3+5])

# Get the string length
print("Length :", len(samp_string))

# Get a slice by saying where to start and end
# The 4th index isn't returned
print(samp_string[0:4])

# Get everything starting at an index
print(samp_string[8:])

# Join or concatenate strings with +
print("Green " + "Eggs")

# Repeat strings with *
print("Hello " * 5)

# Convert an int into a string
num_string = str(4)

# Cycle through each character with for
for char in samp_string:
    print(char)

# Cycle through characters in pairs
# Subtract 1 from the length because length is 1 more then the highest index
# because strings are 0 indexed
# Use range starting at index 0 through string length and increment by
# 2 each time through
for i in range(0, len(samp_string)-1, 2):
    print(samp_string[i] + samp_string[i+1])

# Computers assign characters with a number known as a Unicode
# A-Z have the numbers 65-90 and a-z 97-122

# You can get the Unicode code with ord()
print("A =", ord("A"))

# You can convert from Unicode with chr
print("65 =", chr(65))

# ---------- PROBLEM : SECRET STRING ----------
# Receive a uppercase string and then hide its meaning by turning
# it into a string of unicodes
# Then translate it from unicode back into its original meaning

norm_string = input("Enter a string to hide in uppercase: ")

secret_string = ""

# Cycle through each character in the string
for char in norm_string:

    # Store each character code in a new string
    secret_string += str(ord(char))

print("Secret Message :", secret_string)

norm_string = ""

# Cycle through each character code 2 at a time by incrementing by
# 2 each time through since unicodes go from 65 to 90
for i in range(0, len(secret_string)-1, 2):

    # Get the 1st and 2nd for the 2 digit number
    char_code = secret_string[i] + secret_string[i+1]

    # Convert the codes into characters and add them to the new string
    norm_string += chr(int(char_code))

print("Original Message :", norm_string)

# ---------- SUPER AWESOME MIND SCRAMBLING PROBLEM ----------
# Make the above work with upper and lowercase with 1 addition and
# 1 subtraction

# Add these 2 changes

# secret_string += str(ord(char) - 23)

# norm_string += chr(int(char_code) + 23)