5.9 Searching Sequences

  • Searching is the process of locating a particular key value.

List Method index

  • Searches through a list from index 0 and returns the index of the first element that matches the search key.
  • ValueError if the value is not in the list.
In [1]:
numbers = [3, 7, 1, 4, 2, 8, 5, 6]
In [2]:
numbers.index(5)
Out[2]:
6
In [3]:
numbers *= 2
In [4]:
numbers
Out[4]:
[3, 7, 1, 4, 2, 8, 5, 6, 3, 7, 1, 4, 2, 8, 5, 6]
In [5]:
numbers.index(5, 7)
Out[5]:
14
  • Look for the value 7 in the range of elements with indices 0 through 3.
In [6]:
numbers.index(7, 0, 4)
Out[6]:
1

Operators in and not in

  • Operator in tests whether its right operand’s iterable contains the left operand’s value.
In [7]:
1000 in numbers
Out[7]:
False
In [8]:
5 in numbers
Out[8]:
True
  • Operator not in tests whether its right operand’s iterable does not contain the left operand’s value.
In [9]:
1000 not in numbers
Out[9]:
True
In [10]:
5 not in numbers
Out[10]:
False

Using Operator in to Prevent a ValueError

In [11]:
key = 1000
In [12]:
if key in numbers:
    print(f'found {key} at index {numbers.index(search_key)}')
else:
    print(f'{key} not found')

1000 not found

Built-In Functions any and all

  • Built-in function any returns True if any item in its iterable argument is True.
  • Built-in function all returns True if all items in its iterable argument are True.
  • Nonzero values are True and 0 is False.
  • Non-empty iterable objects also evaluate to True, whereas any empty iterable evaluates to False.

©1992–2020 by Pearson Education, Inc. All Rights Reserved. This content is based on Chapter 5 of the book Intro to Python for Computer Science and Data Science: Learning to Program with AI, Big Data and the Cloud.

DISCLAIMER: The authors and publisher of this book have used their best efforts in preparing the book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The authors and publisher make no warranty of any kind, expressed or implied, with regard to these programs or to the documentation contained in these books. The authors and publisher shall not be liable in any event for incidental or consequential damages in connection with, or arising out of, the furnishing, performance, or use of these programs.