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# Tuesday, January 28th Lecture

  # Given a list, print out all elements of the list
# that ar less than 5

my_list = [8, 1, 1, 7]

# go through every element
# for each elemnt
# check its value
# if less than 5 print it
# if not less than 5, skip it
# go to the next element
num_el = len(my_list)
print("There are", num_el, "in the list")
i = 0
while i < num_el: # stop when at the end of the list
# print("Index", i)
# WHILE BLOCK
# get each element
print("Index", i, "->", my_list[i])
# check its value
if my_list[i] < 5: # if less than 5 print it
print("Found", my_list[i])
# else:
# go to the next element
i = i + 1 # i += 1

• highlight whole region you want to comment and go to ‘FORMAT’–> ‘COMMENT OUT REGION’
• another way to comment out chunks of code: use “”” in the beginning and end
    my_list = [3, 4, 5]
num_el = len(my_list)
print("There are", num_el, "in the list")

i = 0
while i < num_el : # stop when at the end of the list
new_list = []
print("Index", i, "->", my_list[i])
if my_list[i] < 5:
new_list.append(my_list[i])
i += 1
print(new_list)

• OUTPUT: index out of range
    my_list = [3, 4, 5]
num_el = len(my_list)
print("There are", num_el, "in the list")

new_list = []
i = 0
while i < num_el : # stop when at the end of the list
i += 1
if my_list[i] < 5:
new_list.append(my_list[i])
print(new_list)


# Thursday, January 30th Lecture

## Announcements

• If you are struggling a lot, try to get help ASAP. It’s going to get more difficult from here

• Q: How do I contact prof k on piazza?

• A: If you click “instructors”, it will be visible to all the instructors and only the instructors.

## In-class participation quiz

• Hopefully for questions that you didn’t know how to write in Python, you still wrote a pseudocode

### 0)

x_var = 2 #integer


### 1)


name = input(“name:”)
age = input(“age:”)
age = int(age)
print( ‘Hello, ‘, name ,“! ” , “Twice your age is “ , age*2, sep = ‘’)



Or


name = input("name:")
age = input("age:")
age = int(age)
print( "Hello, " + name + "!" +  "Twice your age is " + str(age*2))
#  Note: if you use the + operators, you must convert your age back into a string!!!


Q: What if the person types their age as a string?
A: An error will occur.

Q: Could I use an eval function (if they entered “18” as a string)?
A: Yes, but eval can be dangerous.

### 2)

if N % 2 == 0:
print(“Even”)
else:
print(“Odd”)



Or

if N % 2 != 0:
print("Odd")
else:
print("Even")


• General Note: after a conditional statement, there must be a colon. In the following lines, anything indented is within that conditional statement.

### 3)

Think through the pseudocode. Start with a function name. What does the function take in as a parameter? Next:

def less_than5(lst):
# go thru. all elements of lst
# get the element
# check if <5
# if < 5, print(element)
# do I need an else statement? No. B/c if it doesn’t satisfy the if, it will continue to loop through


my_nums = [1,1,2,3,5,8,13,21,34,55,98]
def less_than5(lst):
'''
Given a list, print out all of the elements that are less than 5.
TODO: Return the list with those elements.
'''
i = 0 # is a conventional variable used for indexing
while ( i < len(lst)):# go thru. all elements of lst. Stop after last element
elt = lst[i]
if elt < 5:
print( "found", elt)
# print("Index",i, "is", elt) # this will show the index position for each iteration
i += 1 # Note: you must have the increment after you use the indexing



another way to do this is using pass Generally, it is best to format your code in a way that you never need to use pass, but this is an example of how it works:

def less_than5(lst):
elt = lst[i]
if lst[i] >= 5:# check if element is >=5. Ignore if >=5
pass # used when a block of code is not supposed to do anything
else:
print( "found", elt)
i += 1

• We will be working with while loops for a while so that we can understand how it and the for loops work.

• Q: How to print out the sum of all the (number) elements in a list?

• sum([1,2,3,4])
• For the lab (lab02), do not use the sum function.

Q: Is pass the same thing as return?
A: No. The return exits out of the function. The pass just exits out of that one block and continues to the rest of the code.