Learn to Program 4
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
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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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