The Basics

Learn the basics of the Python programming language. Numbers, strings, comparisons and variables.

Look at each question and see if you can answer it, then check with the answer we’ve given. Do try these out in the The Python REPL.

Remember: understanding is the most imporant thing, don’t move on until you really understand the question and answer.

What’s this?

  • It’s a number. The number one. In Python we often use numbers and they are really simple to include in our programs.

Is this a number?

  • Yes, a big one.

What about this, still a number?

  • Yes, that’s a float, which means a floating point number, a bit bigger than 1.

If 1.2874 is a float what type of number is 123?

  • It is an int, which means integer or whole number.

What type of number does this expression produce?

  • It produces an int because 9/3 equals 3 exactly.

What type of number is produced here?

  • It produces a float because 1/3 is (very nearly) equal to 0.3333333333333333.

What’s this?

  • It is a string, a sequence of characters.

Is this a string?

  • It is also a string but with just one character. In Python you can use or to mark strings.

Is this a string?

  • No, we start it with a but don’t finish it. Python lets us know with an exception: SyntaxError: EOL while scanning string literal

What about this, is it a string?

'one two three four five"
  • No, somehow we changed our mind whether to use or . We have to use the same one at the start and end of the string.

What happens if we do this?

'hello' + 'world'
  • + can join two strings together. It produces the string ‘helloworld’.

How would we get a space in that string?

  • We could do one of the following:

    'hello' + ' ' + 'world'
    'hello ' + 'world'
    'hello' + ' world'

Did you remember to try these out in the The Python REPL?

What does this expression produce?

2 == 1+1
  • It tests whether 2 equals the result of 1+1. It does so it produces True .

Is this True?

16 == 4*4
  • Yes, 16 is the square of 4.

What about this expression? Is this True?

'16' == 16
  • No, False. A string can never be equal to a number, they are different types.

What does this mean, and is it True?

5 > 1
  • It tests if 5 is greater than 1, and it is so it produces True.

What about this expression, True or False?

5*5 > 4*4 > 3*3
  • Well the square of 5 is bigger than the square of 4 and that is bigger than the square of 3 so this expression produces True.

Here’s a tricky one, what does this produce?

5 > 'five'
  • This won’t work in Python. It raises an exception, a TypeError, we’re told that: ‘>’ not supported between instances of ‘int’ and ‘str’
  • That’s good to know!

What is this?

  • It is not yet defined. Python tells us this with a NameError.

Does this make more sense?

v = 2
  • Yes, v is now a variable and we set it to the value 2. We then ask for the cube of v and this produces 8.

What does this do?

greeting = 'hello'
name = 'eric'
greeting + ' ' + name
  • It creates two variables, one with a greeting and the other with a name. It then joins the two together with a space and produces ‘hello eric’.

What about this, what does it do, and what does it produce?

greeting = 'Hello'
name = input('Enter your name: ')
greeting + ' ' + name
  • It creates a greeting variable with a string, then creates a name variable using whatever the user types at the prompt. It then produces a string containing a greeting for the user.

Things are getting a bit more complicated now! Do try these out in the The Python REPL?

What does this do?

v = 5
v = v - 1
  • It creates a variable called v and sets it to 5 and then produces the square of 5 which is 25, it then reduces v by one so that it becomes 4 and produces the square of this which is 16.

How could we produce all the square numbers between 25 and 1?

v = 5
v = v - 1
v = v - 1
v = v - 1
v = v - 1

That’s a lot of work to produce 5 numbers! Python has a better way, you’ll find out how in the next section Loops.