Lesson 3

Question 1

What does it mean for something to be an iterable in Python?

Answer 1

it means that individual elements can be accessed, individually, making them amenable for use in a loop

Question 2

General form of a for loop:

Answer 2

for my_value in my_seq
code bloc

where my_value represents individual elements in my_seq and my_seq represents multi-element data object, such as a text string or list

code block represents one or more python statements that are executed one time for each element in my_seq

Question 3

for loop take each element of _____, assigns it to _____, and then prints the value of _____

Answer 3

multi-element object (string or list), a variable, the variable

Question 4

What are to important elements of the syntax of a for loop?

Answer 4

-the line defining the loop ends with a colon
-the code block executed by the loop is indented

Question 5

What will the following program output:

my_seq = ‘GATCCTAG’
new_seq = ‘ ‘
for base in my_seq:
new_seq += base + ‘_’
print(new_seq)

Answer 5

G_A_T_C_C_T_A_G
so each time the code runs, the current new_seq gets the base and and underscore added

Question 6

How is the output from this:

my_seq = ‘GATCCTAG’
new_seq = ‘’
for base in my_seq:
new_seq += base + ‘_’
print(new_seq)

different from the output for this:
my_seq = ‘GATCCTAG’
new_seq = ‘’
for base in my_seq:
new_seq += base + ‘_’
print(new_seq)

Answer 6

Because in the first example, the print statement is not in the loop, new_seq is not set back to the empty string at each iteration of the loop, so everything just gets printed out in one line

In the second example, because the print statement is part of the loop, new_seq gets reset to the empty string each time, resulting in each base being printed on a new line with an underscore beside it

Question 7

write a list that contains Alice, Jane, Mary, and Pat

Answer 7

my_list = [‘Alice’, ‘Jane’, ‘Mary’ , ‘Pat’]

Question 8

What is the necessary syntax for lists?

Answer 8

The info is in square brackets and separated by commas

Question 9

What types of data can be contained in a list?

Answer 9

strings (make sure to use quotes!), integers, floating point numbers, and even other lists

Question 10

If you have a list in a list, what is the format of the output?

Answer 10

has double square brackets on either end and has single square brackets separating each list

[[‘a’,’b’,’c’][1,2,3,4]]

Question 11

How to concatenate two lists

Answer 11

use + sign

Question 12

If you concatenate [1,2,3,4] + [‘a’,’b’,’c’] what is the output?

Answer 12

[1,2,3,4, ‘a’,’b’,’c’]

Question 13

What happens if you do 2*list2?
list2=[‘a’,’b’,’c’]

Answer 13

[‘a’,’b’,’c’,’a’,’b’,’c’]

Question 14

Does order matter when multiplying lists?

Answer 14

no

Question 15

if you do my_list[2:4] what do you get?
[‘Alice’, ‘Jane’, ‘Mary’ , ‘Pat’]

Answer 15

[‘Mary’,’Pat’]

Question 16

if you do my_list[0], what do you get? [‘Alice’, ‘Jane’, ‘Mary’ , ‘Pat’]

Answer 16

‘Alice’

Question 17

When a single element is specified in brackets after a list what happens? What about when you specify something in a slice even if it returns only one element?

Answer 17

first part: you get just that element, ex: ‘Alice’
second part: you get the element, but as a list [‘Mary’]

Question 18

How would you interpret list5 [1][1:4]?

Answer 18

Look for elements 1-3 in whatever element 1 in list 5 is. Even if list 5 is another list, you still look at element 1 in it!

Question 19

Are lists mutable?

Answer 19

YES

Question 20

How can you change an element in a list?
list4= [1,2,3, ‘a’,’b’,’c’]

Answer 20

list4 [3] = [‘A’]
this replaces ‘a’ with ‘A’

Question 21

How do you replace more than one element in a list at the same time?

Answer 21

list4[3:6] = [‘A’,’B’,’C’] can also do list4[3:6] = [‘A’] and a single ‘A’ will be put in

Question 22

what does the method append do?

Answer 22

adds an item to the end of a list

Question 23

how to use the append method

Answer 23

list1.append(‘six’)

Question 24

What happens if a list is used as the argument in the append method?

Answer 24

the list is added in brackets and everything so would be added as [6,7,8] exactly even if its being added to another list- would look like [1,2,3,4,5,[6,7,8]]

Question 25

How do you remove items from a list?

Answer 25

use the pop method- list.pop()

Question 26

What happens if no argument is provided in list.pop()?

Answer 26

the last element in the list is removed at the list.pop() method will return that last element by itself

Question 27

How do you insert elements into a list?

Answer 27

use the .insert() method

Question 28

Describe the syntax for the .insert(method)

Answer 28

the first argument in parentheses is the position before the element to be inserted

the second argument is the element to be inserted

so list1.insert(3, ‘two’) puts ‘two’ into position 4 (start counting with 1, so this gets put after the third element)