Python’s membership operators evaluate whether or not a variable exists in a specified sequence. There are two membership operators, as shown in the table that follows

Membership Operator |
Description |

in |
It evaluates to `true` if it finds a value in the specified sequence; it evaluates to `false` otherwise. |

not in |
It evaluates to `true` if it does not find a value in the specified sequence; it evaluates to `false` otherwise. |

Next are some examples of Boolean expressions that use membership operators.

`x in [3, 5, 9]`

. This can be read as “*test if**x**is equal to 3, or equal to 5, or equal to 9*”. It can be written equivalently as

`x == 3 or x == 5 or x == 9`

`s in "ace"`

. This can be read as “*test if the content of variable*`s`

*appears in the word “ace” or in other words, test if*`s`

*is equal to letter “a”, or equal to letter “c”, or equal to letter “e”, or equal to word “ac”, or equal to word “ce”, or equal to word “ace”.*It can be written equivalently as

`s == "a" or s == "c" or s == "e" or s == "ac" or s == "ce" or s == "ace"`

Notice: Please note that the Boolean expression`s in "ace"`

does not check whether or not`s`

is equal to “ae”. It only checks for the presence of the content of variable`s`

within the specified sequence of letters in the word “ace”.

`s not in ["a", "b"]`

. This can be read as “*test if**x**is*It can be written equivalently as**not**equal to letter “a”, nor equal to letter “b”.

`not(s == "a" or s == "b")`

or as

`s != "a" and s != "b"`