1.5 Comparison operators

In Expressions,you learned that Python has arithmetic operators: +, /, - and * and that expressions such as 5 + 2 evaluate to a value (in this case the number 7).

Figure 6

Python also has what are called comparison operators, these are:

Expressions involving these operators always evaluate to a Boolean value, that is  or . Here are some examples:

The comparison operators can be used with other types of data, not just numbers. Used with strings they compare using alphabetical order. For example:

'aardvark' < 'zebra' evaluates to True

In Calculating over columns you saw that when applied to whole columns, the arithmetic operators did the calculations row by row. Similarly, an expression like  will compare the country names, row by row, against the string 'K' and record whether the result is  or  in a series like this:

If such an expression is put within square brackets immediately after a dataframe’s name, a new dataframe is obtained with only those rows where the result is . So:

df[df['Country'] >= 'K']

returns a new dataframe with all the columns of but with only the rows corresponding to countries starting with K or a letter later in the alphabet.

As another example, to see the data for countries with over 80 million inhabitants, the following code will return and display a new dataframe with all the columns of  but with only the rows where it is  that the value in the  column is greater than 

df[df['Population (1000s)'] > 80000]