1. String Manipulation Part 1

2. String Manipulation
Previously, we saw that we could concatenate strings and perform string repetitions
Full_name = “Donald ” + “The Man ” + “Seok”
Lyrics = “I know” * 8

3. String Manipulation
We were also able to compare strings, and convert other data types into strings and also count the length of a string
if “animal” > “apple”:
print(“animal will come before apple in the dictionary”)
x = str(43.95)
print( len( “Donald” ) )

4. String Manipulation
Sometimes, we will need to access individual characters in a string
We can do this by using a for loop, which will iterate the number of times equivalent to the length of a string
Through each iteration, your target variable will hold a different character value, in order of the string

5. String Manipulation
for x in “Donald”: print (x) >> D o n a l d

6. Programming Challenge
Write a program that counts the number of “S”s there are in the string:
“Sally Sells Seashells By The Sea Shore”
Your program should count upper case and lower case “s”s the same way

7. Updating Strings
However, you cannot directly update a string while iterating over it through a for loop
Name = “Donald”
for x in Name:
x = “A”
print (Name)
>> Donald

8. Updating Strings You can achieve this task by creating a new variable
Name = “Donald”
NewName = “”
for x in Name:
NewName += “A”
print(Name, NewName)
>> Donald AAAAAA

9. Indexing
We can also analyze individual elements in a string by a method called “indexing”
We can call any specific character in a string by calling it’s variable name followed by brackets with an integer denoting the place of the character
word = “Donald”
print(word[2])
>> n

10. Indexing Indexes always start with the zero value
Therefore the first character in a string can be denoted as the “0th value”
The index of the last character is denoted by the length of the string minus one

11. Indexing
# S u p e r m a n # word = “Superman” print(len(word)) print(word[0]) >> 8 S

12. Indexing Negative indexes work backwards
So -1 will denote the last character in a string, -2 will denote the second to last character, etc.
number = “456”
print(number[-1], number[-2], number[-3], sep = “”)

13. Indexing
If you use an integer index value that is greater than the length of the word, you will raise an exception
word = “Superman”
print(word[10])
# error!

14. Programming Challenge
Define a function that accepts two arguments: a string literal and a single character.
Have the function return the number of times you find the specified character within the string literal.
Then use the function to ask the user what character they would like to search for in a word / phrase and print out the result

15. Programming Challenge
Write a program that counts the number of vowels found in a particular word / phrase
Use your function from the previous challenge

16. Programming Challenge: Pig Latin
In Pig Latin, the first letter of each word is removed and re-attached to the end of the string with the additional “ay”
Create a function that converts words into Pig Latin
Example:
hello  ellohay

17. Programming Challenge
Write a program that asks the user for a word and finds the letter that is closest to the end of the alphabet in the string
Example:
zelda  z
peach  p
apple  p
Write a program that finds the letter closest to the beginning of the function

18. Min/Max Functions
Python has two built in functions that obtain the maximum and minimum characters in a string (based on their ASCII code)
Example:
a = max(“python”)
b = min(“python”)
print(“max:”, a)
print(“min:”, b)
>> max: y
min: h

19. Strings are Immutable
As we discussed briefly, strings are an immutable data type, meaning that once they are created, they cannot be changed
Although we’ve rewritten variables to hold different values, Python simply points at a separate string in your computer’s memory, then holding that new value
name = “Donald”
name = “Seok”

20. Strings are Immutable
We saw that we can use indexing to pull out single characters from strings but they weren’t necessarily changing the string, rather we created new ones with the values of the characters we pulled out

21. Slicing Strings
Now, we’ll see how we can extract multiple characters or a portion of a string out at a time
We will call this “slicing”
Example:
full_name = “Donald Seok”
first_name = full_name[0:6]
print(first_name)
>> Donald

22. Slicing Strings
In addition, just like the range function, slicing can be done with a step value as well
full_name = “Donald Seok”
new = full_name[0:6:2]
print(new)
>> Dnl

23. Slicing Strings Just a couple of more notes about slicing strings:
- If you omit a starting value, Python will assume that you want to start at the beginning
- Similarly, if you omit an end value, it will assume til the end

24. Practice: Slicing Notation
word = “Superman sings in the shower.” print(word[0:8]) print(word[9:14]) print(word[:5]) print(word[9:]) print(word[-7:]) print(word[0:len(word):3)

25. Practice: Slicing Notation
word = “Superman sings in the shower.” print(word[0:8]) # Superman print(word[9:14]) # sings print(word[:5]) # Super print(word[9:]) # sings in the shower. print(word[-7:]) # shower. print(word[0:len(word):3) # Seasgit or

26. Programming Challenge: Usernames
Let’s say you work at the IT department for NYU and you are asked to generate student ID’s for the incoming freshman class
ID’s are created as follows:
The first four characters of a student’s last name
The first character of a student’s first name
The last two digits of the year in which they graduated high school

27. Programming Challenge: Mirror
Write a function entitled “mirror” that reverses a word and returns it back to the user

28. Programming Challenge: RACECAR
A palindrome is a word that when spelled backwards is still the same word
Write a program that asks the user for a word
Determine whether the word is a palindrome