Searching Dictionaries

With both lists and strings, we used the in and not in operators to search for specific values. These expressions returned either True or False depending on if the value was found in the collection.

Example
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greeting = 'Hello, World!'
fruits = ['apple', 'banana', 'pear', 'kiwi', 'orange']
numbers = [28, 32, 7, 29, 33, 0]

print('or' in greeting)  # Search for the substring 'or' in the larger string.
print('nana' in fruits)  # Search for the value 'nana' in the list of strings.

print('!' not in greeting) # Check if '!' is NOT in 'Hello, World!'.
print(42 not in numbers)   # Check if 42 is NOT in the numbers list.

Console Output

True
False
False
True

Since the elements in a dictionary come as pairs, we search for an item in either the set of keys or the set of values.

We practiced with the keys() and values() methods in the previous two sections, and we can use them in a similar way to search a dictionary.

Example
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ticket_holders = {
    'Bob' : 100,
    'Jessi' : 103,
    'Maria' : 101,
    'Devon' : 102
}

print(101 in ticket_holders.keys())
print(101 in ticket_holders.values())

print('Jessi' in ticket_holders.keys())
print('Jessi' in ticket_holders.values())

Console Output

False
True
True
False
  1. In line 8, 101 in ticket_holders.keys() returns False. Even though 101 is in the dictionary, it is a value, and in this case we are searching through the keys.
  2. In line 9, 101 in ticket_holders.values() returns True.
  3. In lines 11 and 12, we search for the string 'Jessi' first in the keys and then in the values.

Default Search Method

If we do not add the keys() or values() method after the dictionary name, Python searches the keys by default.

This means that

search_value in dictionary_name.keys()

returns the same result as

search_value in dictionary_name