Overview containers: REVIEW THIS!

Name	Create empty	Operators	Important methods
List	[] or list()	[i], in, +, *	append, count, index, insert, pop, remove
Tuple	() or tuple()	[i], in, +, *	count, index
Set	set() only	in	add, pop, remove
Dict	{} or dict()	[k], in	get, items, pop

---

For loops and dictionary: REVIEW THIS!

def dict_example(some_dict):
    for key, value in some_dict.items():
       print(key, "->", value)

dict_example({"color": "blue", "fruit": "apple", "pet": "dog"})
dict_example({1234:"Sharon", 3450:"Ann", 6901:"Robert"})

Number of iterations

# Iterating some determined amount of times using a loop variable
count = 1
while count < limit:
    # Loop body statements go here
    count += 1

OR

for count in range(1, limit)
    # Loop body

- for loops: less likely to enter an infinite loop - while loop: remember to increment sentinel value - while loop: number of iterations is not known prior to execution

---

Review of for loops:

predict the behavior

# Problem 1
for row in range(10):
    print(row, end="\t")
    print("#" * row)

#Problem 2
cities = ["boise", "omaha", "tulsa", "utica"]
result = []
for city in cities:
    result.append(city.upper())
print(result)

# Problem 3
word = "onomatopoeia"
locs = []
for i in range(len(word)):
    if word[i] in ('a', 'e', 'i', 'o', 'u'):
        locs.append(i)
print("Locations:", locs)

---

Another for loop

Notice split()

name = "James Madison University"
words = name.split()
acronym = ""
for word in words:
    letter = word[0]
    print(letter, "is for", word)
    acronym += letter
print(acronym)

---

Go to exercises on the web page

---

def get_short(words):
    short = []
    for word in words:
        if len(word) <= 5:
            short.append(word)
    return short

print(get_short(["hello", "goodbye", "hi", "another", "day"]))

Thonny debugger

• Collatz conjecture

n = int(input("Enter a positive integer: "))
while n != 1:
    print(n)
    if n % 2 == 0:
        n = n // 2
    else:
        n = 3*n + 1
print("n is now 1!")

While Loops

• how are while loops different from for loops?
  • fixed number of times?
• infinite loop
  • boolean expression never evaluates to false
• some execution must occur in the loop body to cause evalution to false

---

For loop

• for is a keyword
• iterates
• iterables
  • list, tuple, set, dictionary, string
• body of the for loop, executed for each iteration

VA_birds = ["mockingbird", "robin", "woodpecker", "cardinal"]
for birdtype in VA_birds:
    print(f'{birdtype} can be found in Virginia')

Body of the for loop

sum = 0
grades = [75, 81, 65, 83, 88]
for grade in grades:
    sum += grade
average = sum/len(grades)
print(f'Your average is {average}')

range()

• generates a sequence of integers
• range object that is immutable
• three values
  • starting integer, default 0
  • ending integer, integers generated up to but not include ending
  • integer step value, default 1 range(4) range(10, 20) range(100, 10000, 50) range(10, 0)

---

for loop with range()

year_started = int(input("enter the year you started at JMU: "))
print("My four years at JMU")
for year in range(year_started, year_started + 4):
    print(year)

checkpoint 1

- write a python for loop to print all the numbers from 1 to 105 that are evenly divisible by 3 and not even

for num in range (1, 106):
    if num % 3 == 0 and num % 2:
        print(num)

for loops and dictionaries

calories = {'apple': 72,
            'bagel': 290,
            'chicken breast' : 150,
            'ice cream' : 160
            }
for food_item in calories:
    print(f'{food_item} has {calories[food_item]} calories')
# same results
for food_item, number in calories.items():
    print(f'{food_item} has {number} calories')

enumerate

• iterate through a sequence
  • index and corresponding element
• combination range() and len()
  • then index into the sequence for value
• enumerate() function
  • pass an iterable (string, list, tuple, set, dictionary)
  • returns an enumerate object
    • adds a counter index to each corresponding element value

---

Checkpoint 2: try these

names = ['Bob', 'Sally', 'John', 'Nathan']
enumerate_info = enumerate(names)
print(names)
print(list(enumerate_info))

• enumerate() yields a new tuple each itertion of the loop

  names = ['Bob', 'Sally', 'John', 'Nathan']
  for who in enumerate(names):
      print(who)
  

---

• enumrate()
  • returns a tuple
  • can be unpacked into two variables

    names = ['Bob', 'Sally', 'John', 'Nathan']
    for order, who in enumerate(names):
        print(order, who)
    

---

Recap of for loops

Code	Meaning
for value in my_list:	for each value in a list
for index in range(len(my_list)):	for each index in a list
for index, value in enumerate(my_list):	for each index and value
for key in my_dict:	for each key in a dict
for key, value in my_dict.items():	For each key and value

---

Other Concepts in this chapter

• incremental programming
• function stubs
  • pass
• keyword function arguments
• default parameter values

---

For Loops with sets

def all_pairs(sentence):
    """Return a set containing all neighboring pairs of letters.

    Args:
        sentence (string): Any string

    Returns:
        set: A set containing all unique pairs of neighboring letters.
    """
    all_pairs = set()
    for i in range(len(sentence) - 1):  # Stop one index *before* the end.
        letter = sentence[i]
        next_letter = sentence[i + 1]
        all_pairs.add(letter + next_letter)
    return all_pairs

print(all_pairs("abbbbcbcbcab"))

output is {'bc', 'ca', 'cb', 'ab', 'bb'}

---