Learn to Program 4

Posted by Derek Banas on Jun 29, 2016 in Web Design | 0 comments

This time in my Learn to Program series we’ll cover many string functions and how they can help use solve complex programming problems. We’ll do more with exceptions. We’ll start to explore lists. We’ll create our first function. And, we’ll create an acronym generator and explore the basics of encryption.

If you missed the first video watch it first. All of the code follows the video. You can expect a new video every Saturday and Wednesday because you guys have asked me to stay on a schedule.

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Code & Transcript

# ---------- STRING METHODS ----------

# Strings have many methods we can use beyond what I covered last time
rand_string = "   this is an important string   "

# Delete whitespace on left
rand_string = rand_string.lstrip()

# Delete whitespace on right
rand_string = rand_string.rstrip()

# Delete whitespace on right and left
rand_string = rand_string.strip()

# Capitalize the 1st letter
print(rand_string.capitalize())

# Capitalize every letter
print(rand_string.upper())

# lowercase all letters
print(rand_string.lower())

# Turn a list into a string and separate items with the defined
# separator
a_list = ["Bunch", "of", "random", "words"]
print(" ".join(a_list))

# Convert a string into a list
a_list_2 = rand_string.split()

for i in a_list_2:
    print(i)

# Count how many times a string occurs in a string
print("How many is :", rand_string.count("is"))

# Get index of matching string
print("Where is string :", rand_string.find("string"))

# Replace a substring
print(rand_string.replace("an ", "a kind of "))

# ---------- PROBLEM : ACRONYM GENERATOR ----------
# You will enter a string and then convert it to an acronym
# with uppercase letters like this
'''
Convert to Acronym : Random Access Memory
RAM
'''

# Ask for a string
orig_string = input("Convert to Acronym : ")

# Convert the string to all uppercase
orig_string = orig_string.upper()

# Convert the string into a list
list_of_words = orig_string.split()

# Cycle through the list
for word in list_of_words:

    # Get the 1st letter of the word and eliminate the newline
    print(word[0], end="")

print()

# ---------- MORE STRING METHODS ----------
# For our next problem some additional string methods are going to be
# very useful

letter_z = "z"
num_3 = "3"
a_space = " "

# Returns True if characters are letters or numbers
# Whitespace is false
print("Is z a letter or number :", letter_z.isalnum())

# Returns True if characters are letters
print("Is z a letter :", letter_z.isalpha())

# Returns True if characters are numbers (Floats are False)
print("Is 3 a number :", num_3.isdigit())

# Returns True if all are lowercase
print("Is z a lowercase :", letter_z.islower())

# Returns True if all are uppercase
print("Is z a uppercase :", letter_z.isupper())

# Returns True if all are spaces
print("Is space a space :", a_space.isspace())

# ---------- MAKE A isfloat FUNCTION ----------
# There is no way to check if a string contains a float
# so let's make one by defining our own function

# Functions allow use to avoid repeating code
# They can receive values (attributes / parameters)
# They can return values

# You define your function name and the names for the values
# it receives like this

def isfloat(str_val):
    try:

        # If the string isn't a float float() will throw a
        # ValueError
        float(str_val)

        # If there is a value you want to return use return
        return True
    except ValueError:
        return False

pi = 3.14

# We call our functions by name and pass in a value between
# the parentheses
print("Is Pi a Float :", isfloat(pi))

# ---------- PROBLEM : CAESAR'S CIPHER ----------
# Receive a message and then encrypt it by shifting the
# characters by a requested amount to the right
# A becomes D, B becomes E for example
# Also decrypt the message back again

# A-Z have the numbers 65-90 in unicode
# a-z have the numbers 97-122
# You get the unicode of a character with ord(yourLetter)
# You convert from unicode to character with chr(yourNumber)

# You should check if a character is a letter and if not
# leave it as its default

# Hints
# Use isupper() to decided which unicodes to work with
# Add the key (number of characters to shift) and if
# bigger or smaller then the unicode for A, Z, a, or z
# increase or decrease by 26

# Receive the message to encrypt and the number of characters to shift
message = input("Enter your message : ")
key = int(input("How many characters should we shift (1 - 26)"))

# Prepare your secret message
secret_message = ""

# Cycle through each character in the message
for char in message:

    # If it isn't a letter then keep it as it is in the else below
    if char.isalpha():

        # Get the character code and add the shift amount
        char_code = ord(char)
        char_code += key

        # If uppercase then compare to uppercase unicodes
        if char.isupper():

            # If bigger than Z subtract 26
            if char_code > ord('Z'):
                char_code -= 26

            # If smaller than A add 26
            elif char_code < ord('A'):
                char_code += 26

        # Do the same for lowercase characters
        else:
            if char_code > ord('z'):
                char_code -= 26
            elif char_code < ord('a'):
                char_code += 26

        # Convert from code to letter and add to message
        secret_message += chr(char_code)

    # If not a letter leave the character as is
    else:
        secret_message += char

print("Encrypted :", secret_message)

# To decrypt the only thing that changes is the sign of the key
key = -key

orig_message = ""

for char in secret_message:
    if char.isalpha():
        char_code = ord(char)
        char_code += key

        if char.isupper():
            if char_code > ord('Z'):
                char_code -= 26
            elif char_code < ord('A'):
                char_code += 26
        else:
            if char_code > ord('z'):
                char_code -= 26
            elif char_code < ord('a'):
                char_code += 26

        orig_message += chr(char_code)

    else:
        orig_message += char

print("Decrypted :", orig_message)

# ---------- EXTRA HOMEWORK ----------
# For homework put the duplicate code above in a function

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# ---------- STRING METHODS ----------

# Strings have many methods we can use beyond what I covered last time

rand_string = " this is an important string "

# Delete whitespace on left

rand_string = rand_string.lstrip()

# Delete whitespace on right

rand_string = rand_string.rstrip()

# Delete whitespace on right and left

rand_string = rand_string.strip()

# Capitalize the 1st letter

print(rand_string.capitalize())

# Capitalize every letter

print(rand_string.upper())

# lowercase all letters

print(rand_string.lower())

# Turn a list into a string and separate items with the defined

# separator

a_list = ["Bunch", "of", "random", "words"]

print(" ".join(a_list))

# Convert a string into a list

a_list_2 = rand_string.split()

for i in a_list_2:

print(i)

# Count how many times a string occurs in a string

print("How many is :", rand_string.count("is"))

# Get index of matching string

print("Where is string :", rand_string.find("string"))

# Replace a substring

print(rand_string.replace("an ", "a kind of "))

# ---------- PROBLEM : ACRONYM GENERATOR ----------

# You will enter a string and then convert it to an acronym

# with uppercase letters like this

'''

Convert to Acronym : Random Access Memory

RAM

'''

# Ask for a string

orig_string = input("Convert to Acronym : ")

# Convert the string to all uppercase

orig_string = orig_string.upper()

# Convert the string into a list

list_of_words = orig_string.split()

# Cycle through the list

for word in list_of_words:

# Get the 1st letter of the word and eliminate the newline

print(word[0], end="")

print()

# ---------- MORE STRING METHODS ----------

# For our next problem some additional string methods are going to be

# very useful

letter_z = "z"

num_3 = "3"

a_space = " "

# Returns True if characters are letters or numbers

# Whitespace is false

print("Is z a letter or number :", letter_z.isalnum())

# Returns True if characters are letters

print("Is z a letter :", letter_z.isalpha())

# Returns True if characters are numbers (Floats are False)

print("Is 3 a number :", num_3.isdigit())

# Returns True if all are lowercase

print("Is z a lowercase :", letter_z.islower())

# Returns True if all are uppercase

print("Is z a uppercase :", letter_z.isupper())

# Returns True if all are spaces

print("Is space a space :", a_space.isspace())

# ---------- MAKE A isfloat FUNCTION ----------

# There is no way to check if a string contains a float

# so let's make one by defining our own function

# Functions allow use to avoid repeating code

# They can receive values (attributes / parameters)

# They can return values

# You define your function name and the names for the values

# it receives like this

def isfloat(str_val):

try:

# If the string isn't a float float() will throw a

# ValueError

float(str_val)

# If there is a value you want to return use return

return True

except ValueError:

return False

pi = 3.14

# We call our functions by name and pass in a value between

# the parentheses

print("Is Pi a Float :", isfloat(pi))

# ---------- PROBLEM : CAESAR'S CIPHER ----------

# Receive a message and then encrypt it by shifting the

# characters by a requested amount to the right

# A becomes D, B becomes E for example

# Also decrypt the message back again

# A-Z have the numbers 65-90 in unicode

# a-z have the numbers 97-122

# You get the unicode of a character with ord(yourLetter)

# You convert from unicode to character with chr(yourNumber)

# You should check if a character is a letter and if not

# leave it as its default

# Hints

# Use isupper() to decided which unicodes to work with

# Add the key (number of characters to shift) and if

# bigger or smaller then the unicode for A, Z, a, or z

# increase or decrease by 26

# Receive the message to encrypt and the number of characters to shift

message = input("Enter your message : ")

key = int(input("How many characters should we shift (1 - 26)"))

# Prepare your secret message

secret_message = ""

# Cycle through each character in the message

for char in message:

# If it isn't a letter then keep it as it is in the else below

if char.isalpha():

# Get the character code and add the shift amount

char_code = ord(char)

char_code += key

# If uppercase then compare to uppercase unicodes

if char.isupper():

# If bigger than Z subtract 26

if char_code > ord('Z'):

char_code -= 26

# If smaller than A add 26

elif char_code < ord('A'):

char_code += 26

# Do the same for lowercase characters

else:

if char_code > ord('z'):

char_code -= 26

elif char_code < ord('a'):

char_code += 26

# Convert from code to letter and add to message

secret_message += chr(char_code)

# If not a letter leave the character as is

else:

secret_message += char

print("Encrypted :", secret_message)

# To decrypt the only thing that changes is the sign of the key

key = -key

orig_message = ""

for char in secret_message:

if char.isalpha():

char_code = ord(char)

char_code += key

if char.isupper():

if char_code > ord('Z'):

char_code -= 26

elif char_code < ord('A'):

char_code += 26

else:

if char_code > ord('z'):

char_code -= 26

elif char_code < ord('a'):

char_code += 26

orig_message += chr(char_code)

else:

orig_message += char

print("Decrypted :", orig_message)

# ---------- EXTRA HOMEWORK ----------

# For homework put the duplicate code above in a function

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Learn to Program 4

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