# 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

### Specifying the Starting Index of a Search¶

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

### Specifying the Starting and Ending Indices of a Search¶

- 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`.

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