Python Projects for Beginners a ten-Week Bootcamp Approach to Python Programming

Deleting Information

Sometimes you’ll need to remove a certain pair. To do so, you’ll need to use the del
function:

# deleting a key/value pair from a dictionary car = { "year": 2018 } try:
del car["year"] print(car) except: print("That key does not exist")

Go ahead and run the cell. Be very careful when deleting key-value pairs. If the key you’re trying to remove doesn’t exist, it will crash the program. To avoid that problem, we use a try/except.

Looping a Dictionary

Dictionaries are iterable like lists. However, they have three different methods for doing so. You can iterate over both the keys and values together, only keys, or only values.
Looping Only Keys
To iterate through a dictionary while only accessing the keys, you’ll use the .keys() method:

# looping over a dictionary via the keys person = { "name": "John", "age": 26 } for key in person.keys( ):
print(key) print( person[key] ) # will output the value at the current key

Go ahead and run the cell. As we iterate over person, our temporary variable of key will be equal to each key name. This still gives us the ability to access each value by using our key variable.
Looping Only Values
When you don’t need to access the keys, using the .values( ) method is best:

# looping over a dictionary via the values person = { "name": "John", "age": 26 } for value in person.values( ): print(value)

Go ahead and run the cell. We won’t have access to the key names, but for this method, we’re only trying to get the values anyways. Our temporary variable value will store each value from the key-value pairs as we iterate over person.
Looping Key-Value Pairs
If you need the ability to access both the key and value, then you’ll want to use the .items() method. This approach will assign two temporary variables instead of one:

# looping over a dictionary via the key/value pair person = { "name": "John", "age": 26 } for key, value in person.items( ):
print( "{ }: { }".format(key, value) )

Go ahead and run the cell. As we iterate over person, the key-value pairs are assigned to their respective temporary variables of key and value. We now have access to both easily.

Note	The temporary variable names are usually called “k” and “v.”