Introduction to Programming - 3

Question 1

What are loops in Python?

Answer 1

allow you to execute a block of code repeatedly based on a condition

Question 2

Loop is a general term for a programming construct which allows us to

Answer 2

do things many times

Question 3

Why is loops good practically? - (2)

Answer 3

might be making lots of stimuli for an experiment or analyzing lots of different datasets.

..or that thing you just did where you printed out the same ‘count’ statement more or less six times

Question 4

2 types of loops in Python - (2)

Answer 4

1. For loop
2. While loop

Question 5

What is For loop?

Answer 5

For loops in Python are used to iterate over a sequence (such as a list, tuple, string, or range) and execute the same block of code for each element in the sequence

Question 6

Loop you will commonly encounter is a

Answer 6

for loop

Question 7

General structure of for loop

Answer 7

Question 8

What does this general structure mean? - (4)

Answer 8

What this means is that LOOPVARIABLE (which can be named whatever you want) will be set to the first item in LIST_OF_THINGS_TO_ITERATE_OVER. The code which is indented (just a comment in this case) will then run.

Once all of the code which is indented has been run, the loop will go back to the top,

LOOPVARIABLE will be set to the second item in LIST_OF_THINGS_TO_ITERATE_OVER and all of the indented code will run again.

This will repeat for each element in LIST_OF_THINGS_TO_ITERATE_OVER.

Question 9

Example of for loop using structure

Answer 9

Question 10

What will be the output?

Answer 10

Hello!
Hello 1
Hello!
Hello 2
Hello!
Hello 3
Hello!
Hello 4
Hello!
Hello 5
Hello!
Hello 6
Hello!
Hello 7
Hello!
Hello 8
Hello!
Hello 9
Hello!
Hello 10

Question 11

In the for loop

The for keyword…

It is followed by…

The keyword in…

Finaly there is :

The code inside te for loop is … - (6)

Answer 11

The for keyword starts the loop.

It is followed by the variable which is created to run the loop.

The keyword in is then used, followed by the expression which gives the list of items over which to iterate.

As we will see later, this is not always a list or tuple - there are other possibilities.

Finally, there is a colon : which shows that the loop is starting.

The code inside the loop is indented. In other words it is shifted to the right - like this line

Question 12

In loops, Python works out where your loop ends by - (2)

Answer 12

looking at the indentation of the text – i.e. it uses spaces. At first this can be confusing but it becomes second nature after a while.

Question 13

To ident code inside loop you can either use

Answer 13

4 spaces or tab

Question 14

Create a for loop that produces 1-10

Answer 14

Question 15

Iterating over a list refers to the process of

Answer 15

accessing each element in the list one by one in a sequential manner.

Question 16

The simplest form of a loop involves

Answer 16

setting up a list and then performing some code for each entry in the list.

Question 17

The simplest form of a loop involves setting up a list and then performing some code for each entry in the list. For example, code below shows..

Answer 17

we print each element in a list followed by itself squared

Question 18

Output of this code and explain - (4):

Answer 18

Meaning:

print(x,x**2) is idented within for loop so we print each element in a list followed by itself squared:

In print(x.5) is not idented within for loop and identation is different from print(x,x2) so left the for loop

print(x,x**.5) square root the last element of the list (‘x’) which is 40 and prints “Done”

Output:
10 100
20 400
30 900
40 1600
6.324555320336759
Done

Question 19

Example of for loop written out in detail/full

Answer 19

Question 20

For loops do not have to be on a single line as we can write:

Answer 20

Question 21

Explain this code and give its output:

Answer 21

Meaning:
The loop iterates over each element in the list my_list.

For each iteration, it prints “Hello”.

It computes the square of the current element (x) and stores it in y.

It then prints both the current element (x) and its square (y).

Output:
Hello
10 100
Hello
20 400
Hello
30 900
Hello
40 1600

Question 22

Long-handed version of the for loop code

Answer 22

Question 23

You can run any code you want inside of a loop. One thing which you should not do however, is to - (2)

Answer 23

delete an item in a list whilst you are looping over the list.

This will cause hard to find problems in your code and almost certainly not do what you want

Question 24

Write a code that has a list 10-100 stored in my_list = [] var

For loop that loops over that list and prints out value of x and its x squared and its square root on each iteration

Answer 24

Question 25

What is output of the code?

Answer 25

Question 26

What is nested for loops? - (3)

Answer 26

situation where one for loop is contained within another for loop. This means that one loop runs inside another loop. Each time the outer loop runs once, the inner loop can potentially run multiple times, depending on its own iteration behavior.

Question 27

For nested for loops it is

Answer 27

important to follow the indentation carefully reading this code.

Question 28

Meaning of this nested for loop example - (13)

Answer 28

As we can see, the first loop uses x as its loop variable. On line 4, this will initially be set to the first value of my_first_list which is 1 (this is represented by x = 1 in the output comments). We then progress to line 5 where we print out the statement Before Y loop starts. On line 7, another loop is constructed. The second loop uses y as its loop variable. You should always use a different loop variable for each nested loop. At this point, y will be set to the first value in my_second_list, which is 50 (this is represented by # y = 50 in the output comments). We then execute the code within the loop on line 8 (the print function call) which prints out the values of both x and y. At this point, we run out of code, so we go back to the innermost loop (line 7) and update y to 60. We run the print again, then update y to 70 and run the print again. We have now finished the "inner" y loop and execute line 10 which prints out the string After Y loop ends. We then go back to line 4 and update the x variable to 2. We now continue to line 5 again, which causes us to go print the Before Y loop starts string and then go around the y loop again, making y equal to 50, 60, and 70 in turn in the same way that we did previously

Question 29

Long-handed version of this for loop

Answer 29

Question 30

Fix the code to simulate all possible sums of two 6-sided dice, Which number is the most common? - (2)

Answer 30

It determines which number is the most common by printing the sum of each pair of throws and then analyzing the results. The most common number should be 7 since there are more combinations of dice throws that sum to 7 than any other number

Question 31

What is range() in Python? - (2)

Answer 31

built-in function used to generate a sequence of numbers. It's commonly used in loops to iterate over a specific range of numbers.

Question 32

3 ways to use/call range() function - (3)

Answer 32

1. range(stop) 2. range(start,stop) 3. range(start,stop,setp)

Question 33

What is range(stop)

Answer 33

This generates a sequence of numbers starting from 0 up to (but not including) the specified stop value.

Question 34

What is range(start,stop)?

Answer 34

This generates a sequence of numbers starting from start up to (but not including) the stop value.

Question 35

What is range(start,stop,step) - (2)

Answer 35

This generates a sequence of numbers starting from start up to (but not including) the stop value, with a specified step size between each number. The step parameter is optional and defaults to 1 if not provided

Question 36

In python, all stop-style parameters are exclusive; i.e. - (3)

Answer 36

they are not included in the list which is returned. This means that if we ask for range(0, 4), we will get the numbers 0, 1, 2, 3. Forgetting how this works is a common source of bugs.

Question 37

What will this output give you? x = range(5) print(type(x)) print(x)

Answer 37

range(0, 5) print the generator

Question 38

What will this code give you? x = list(range(5)) print(type(x)) print(x) 0 it is convert to list and print

Answer 38

[0, 1, 2, 3, 4]

Question 39

What will this code give you? x = list(range(1, 500)) print(x)

Answer 39

[1, 2, 3, 4, 5, ...., 499]

Question 40

The step parameter in range... - (2)

Answer 40

sets the increment or decrement. Setting this to be negative lets us count backwards.

Question 41

What will these code give? - (3)

Answer 41

[1, 3] [5, 4, 3, 2, 1] [4, 3, 2, 1, 0]

Question 42

range function generates a sequence of integer numbers within a specified range. If you want to use floating point numbers then

Answer 42

use the arange function from the numpy module – we will cover this in a future session.

Question 42

Exercise: Write python code, using a loop, to count between -10 and 10 (inclusive) and for each number print out the number and its cube (i.e. the number to the power 3).

Answer 42