Python Basics Recap

Last updated on 2026-04-21 | Edit this page

Overview

Questions

  • Python Refresher

Objectives

  • Understanding key concepts in Python

This course follows on from the python introduction course. To ensure that we are starting from similar positions, there follows a short multiple choice quiz on key python concepts that we will be building on through this course.

Variables and Lists

Challenge

1. Assigning a value to a variable

We wish to store the string Cat as a value in the variable animal, which of these lines of code will do this for us?

  1. animal = 'Cat'
  2. animal = Cat
  3. Cat = animal
  4. animal(Cat)

Answer 1 is correct

Challenge

2. Assigning values to a list

We wish to create a list of values, which of these lines of code is valid to do this?

  1. varlist = [34, 57, '2d']
  2. varlist = (12, 'vr', 95)
  3. varlist = 'xcf', 12, 97

Answer 1 is correct

Challenge

3a. Indexing characters in a string

Lists and strings both contain multiple indexed values (in the case of strings these are specifically individual characters rather than other values). If we have a variable animal which contains the string penguin, which of these options will print the first character (p) for us?

  1. print(animal[0])
  2. print(animal[1])
  3. print(animal['p'])

Answer 1 is correct

Challenge

3b. Indexing characters in a string (slicing)

We can also select whole sections of lists and strings, not just single elements. Using the same variable animal, containing the string penguin, as above, which of these options will print the last 2 characters for us? (Note that there is more an one correct answer)

  1. print(animal[5:])
  2. print(animal[6:])
  3. print(animal[6:7])
  4. print(animal[5:7])
  5. print(animal[-2:])
  6. print(animal[:-2])

Answers 1, 4, and 5 are correct

Loops

Challenge

4. Constructing a for loop

Please write a simple for loop which will print out each of the characters in the animal variable one at a time.

PYTHON 

for char in animal:
    print(char)

Software Modules

Challenge

5. Loading new functions

We want to use the functions in the numpy library in our code. How do we open this library in our code?

  1. import numpy
  2. load numpy
  3. open numpy

Answer 1 is correct

If statements and conditionals

Challenge

6. Conditionals

Which of these conditional tests returns a True result?

  1. 4 > 3
  2. 'a' != 'b'
  3. 6 >= 6.0
  4. '3' == 3
  5. 3 > 'c'

Answers 1, 2, and 3 return True results. 4 returns False. 5 raises an Error.

Challenge

7. If statements

What is printed when this if statement is used?

PYTHON 

if 4 > 5:
    print('A')
elif 4 <= 5:
    print('B')
elif 4 < 5:
    print('C')
else:
    print('D')
  1. A
  2. B
  3. C
  4. B and C
  5. D
  6. A and D

B. Both 4 <= 5 and 4 < 5 would return a True result, but the if statement is exited as soon as the True result is returned.

Callout

Formatting Variables and Objects in Strings

Throughout this course, we will be printing the values of variables inside strings to demonstrate what the code does. There are a number of ways to this in Python; in this course we will be using f-strings which are the recommended string interpolation syntax from version 3.6 onwards.

To use f-strings simply start a string literal with f or F, then embed whatever you want interpolating into the string within curly braces {}:

PYTHON 

two_int = 2
two_str = "2"
f_string = f"{two_int} + {two_str} = {2 + 2}"
print(f_string)

OUTPUT 

2 + 2 = 4

Numerical values can be formatted using : inside the curly braces. For example, an integer i can be made to have a width n using {i:nd}, or {i:0nd} to pad it out with zeros:

PYTHON 

print(f"One with four leading spaces {1:5d}")
print(f"One with four leading zeros {1:05d}")

OUTPUT 

One with four leading spaces     1
One with four leading zeros 00001

Floating point variables can have their precision specified with a number after a decimal point and an f:

PYTHON 

pi = 3.141592653589793
print(pi)
print(f"pi to three decimal places is {pi:.3f}")

OUTPUT 

3.141592653589793
pi to three decimal places is 3.142

Or made to use scientific notation with an e:

PYTHON 

print(1e9)
print(f"A billion in scientific notation is {1e9:.1e}")

OUTPUT 

1000000000.0
A billion in scientific notation is 1.0e+09

This is only scratching the surface of what you can do with f-strings, they are often the most powerful and concise way to format variables inside strings. However, there are occasions when other methods are preferable, and you should be careful using them with Python before version 3.12.

To learn more, see: Python f-strings.

Generative AI

We would like to reiterate the Carpentries stance on Generative AI in coding which you may have seen when preparing for this course.

To summarise the position, the recommendation is that you avoid getting help from generative AI during the workshop for several reasons:

  • For most problems you will encounter at this stage, help and answers can be found among the first results returned by searching the internet or looking on e.g. StackOverflow.
  • The foundational knowledge and skills you will learn in this lesson by writing and fixing your own programs are essential to be able to evaluate the correctness and safety of any code you receive from online help or a generative AI chatbot. If you choose to use these tools in the future, the expertise you gain from learning and practising these fundamentals on your own will help you use them more effectively.
  • As you continue programming, the mistakes you make will be the kinds that have also been made – and overcome! – by everybody else who learned to program before you. Since these mistakes and the questions you are likely to have at this stage are common, they are also better represented than other, more specialised problems and tasks in the data that was used to train generative AI tools. This means that a generative AI chatbot is more likely to produce accurate responses to questions that novices ask, which could give you a false impression of how reliable they will be when you are ready to do things that are more advanced.
Key Points
  • Assign values to variables using =
  • Generate lists using square brackets []
  • Use indexes inside [], starting at 0, to select characters from strings and items from lists
  • Use for to loop through items in iterable objects
  • Make conditional expressions using ==, !=, >, <, >= and <=
  • Use f'{}' to embed formatted variables inside strings
  • Avoid use of generative AI for this course