29. What's your name?

We have seen how we could assign numbers to variables. We can also assign strings to variables; for example:

>>> FirstName = "Andre"
>>> LastName = "Roberge"
>>> FullName = FirstName + LastName
>>> print FullName
AndreRoberge

Notice how the "plus sign" (+) is used by Python to combine two strings into one; this operation is called a string concatenation. However, notice how there is no space between the first and last name. We can correct this by adding in between a third string composed of a single space character.

>>> FullName = FirstName + " " + LastName
>>> print FullName
Andre Roberge

Another way to obtain the same result is to use the %s notation we had used for putting numerical variables inside a string.

>>> name = "%s %s" % (FirstName, LastName)
>>> print name
Andre Roberge

Finally, we can compare and see if both strings are equal.

>>> print name == FullName
True

Try it on your own!

Slices

Sometimes, we only want to use a single character in a string, on a small part of a string (called a substring). To do this, it is useful to learn about slicing.

I will give you three rules to remember, and a hint about the notation, and then give you the result of a whole series of examples that you can try on your own with the Python interpreter. Other than the three rules, I will not give you any other explanation for this section, so you will have to look at it very carefully to completely understand what is going on.

1. Python starts counting at zero.
2. Python doesn't include what you would expect to be the last number when it counts.
3. Python can count by steps.

Useful notation: [first:last:step]; all three are optional.

Here are the examples:

>>> alphabet = "abcdefghijklmnopqrstuvwxyz"
>>> digits = '0123456789'

>>> alphabet[0]
'a'

>>> alphabet[1]
'b'

>>> alphabet[5]
'f'

>>> digits[0]
'0'

>>> digits[7]
'7'

>>> digits[-1]
'9'

>>> digits[-2]
'8'

>>> alphabet[-3]
'x'

>>> digits[0:3]
'012'

>>> digits[0:4]
'0123'

>>> digits[0:5]
'01234'

>>> digits[2:5]
'234'

>>> alphabet[2:5]
'cde'

>>> digits[0:10:2]
'02468'

>>> digits[0::2]
'02468'

>>> digits[0::3]
'0369'

>>> digits[::3]
'0369'

>>> digits[::-1]
'9876543210'

>>> digits[::-2]
'97531'

>>> digits[::-3]
'9630'

>>> alphabet[:10:2]
'acegi'

Make up your own strings and try a few more examples by yourself!

Variables and functions - - Object-Oriented Programming: "dot" notation