5.15 Other Sequence Processing Functions

Finding the Minimum and Maximum Values Using a Key Function

In [1]:
'Red' < 'orange'
Out[1]:
True
  • 'R' “comes after” 'o' in the alphabet, so you might expect 'Red' to be less than 'orange' and the condition above to be False.
  • Strings are compared by their characters’ underlying numerical values, and lowercase letters have higher numerical values than uppercase letters.
  • Confirm with built-in function ord:
In [2]:
ord('R')
Out[2]:
82
In [3]:
ord('o')
Out[3]:
111
In [4]:
colors = ['Red', 'orange', 'Yellow', 'green', 'Blue']
  • Assume that we’d like to determine the minimum and maximum strings using alphabetical order.
  • Can specify sort order with the key argument.
In [5]:
min(colors, key=lambda s: s.lower())
Out[5]:
'Blue'
In [6]:
max(colors, key=lambda s: s.lower())
Out[6]:
'Yellow'

Iterating Backwards Through a Sequence

In [7]:
numbers = [10, 3, 7, 1, 9, 4, 2, 8, 5, 6]
In [8]:
reversed_numbers = [item ** 2 for item in reversed(numbers)]
In [9]:
reversed_numbers
Out[9]:
[36, 25, 64, 4, 16, 81, 1, 49, 9, 100]

Combining Iterables into Tuples of Corresponding Elements

  • Built-in function zip enables you to iterate over multiple iterables of data at the same time.
  • Receives any number of iterables and returns an iterator that produces tuples containing the elements at the same index in each.
In [10]:
names = ['Bob', 'Sue', 'Amanda']
In [11]:
grade_point_averages = [3.5, 4.0, 3.75]
In [12]:
for name, gpa in zip(names, grade_point_averages):
    print(f'Name={name}; GPA={gpa}')

Name=Bob; GPA=3.5
Name=Sue; GPA=4.0
Name=Amanda; GPA=3.75
  • Shortest argument determines the number of tuples produced.

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