If you’re a Python programmer, then you know that dictionaries are an essential data structure in the language. They allow you to store and retrieve key-value pairs quickly and efficiently, making them perfect for many different types of applications. However, there’s more to working with dictionaries than simple insertion and retrieval! In this blog post, we’ll explore ten useful Python dictionary methods that will help take your programming skills to the next level. From updating values to merging multiple dictionaries together, these tips are sure to make your code even more powerful and effective. So if you’re ready to learn some new tricks for working with one of Python’s most important data structures, then let’s dive in!
Get the Dictionary Keys with keys()
The keys() method in Python returns a list of all the keys in a dictionary. You can use this method to get a list of all the keys in a dictionary, or to check if a key exists in a dictionary. If you want to get the values of a dictionary, you can use the values() method.
If you have a dictionary named my_dict, you can get a list of all the keys in the dictionary with my_dict.keys().
Get the Dictionary Values with values()
The Dictionary data structure is very powerful in Python. In this article, we’ll go over the .values() method, which is one of the most useful methods for dictionaries.
The .values() method returns a list of values from a dictionary. This is different than the keys() method, which returns a list of keys. Let’s take a look at an example:
“`python
greek_letters = {
‘alpha’: ‘a’,
‘beta’: ‘b’,
‘gamma’: ‘g’
}
“`
If we use the .values() method on our dictionary, we’ll get back a list of values:
>>> greek_letters.values()
[‘a’, ‘b’, ‘g’]
This can be useful if you want to iterate over all of the values in a dictionary:
>>> for letter in greek_letters.values():
… print(letter)
…
a
b
g
Or if you want to check if a certain value is in the dictionary:
>>> if ‘a’ in greek_letters.values():
… print(“Found it!”)
Found it!
Get Key-Value Pairs with items()
The dictionary method items() returns a list of key-value pairs in the dictionary. This is useful when you want to iterate over the keys and values in the dictionary.
For example, if you have a dictionary called my_dict, you can get a list of key-value pairs with the following code:
my_dict = {‘key1’: ‘value1’, ‘key2’: ‘value2’, ‘key3’: ‘value3’}
for key, value in my_dict.items():
print(key + “: ” + value)
This would print out the following:
key1: value1
key2: value2
key3: value3
Get a Shallow Copy with copy()
The copy() method returns a shallow copy of a dictionary. A shallow copy is a new dictionary that contains the same key-value pairs as the original dictionary, but the new dictionary stores these key-value pairs in different memory locations than the key-value pairs in the original dictionary.
This is important to know because if you mutate (change) a value in the copy, the value in the original dictionary will not be changed. However, if you mutate a value in the original dictionary, the value in the copy will also be changed, because both dictionaries are storing their values in the same memory location.
Here’s an example:
>>> d1 = {‘a’: 1, ‘b’: 2}
>>> d2 = d1.copy()
>>> d2[‘a’] = 3 # Mutating a value in d2 does not change d1
>>> d1
{‘a’: 1, ‘b’: 2}
>>> d2
{‘a’: 3, ‘b’: 2}
>>> d3 = {‘a’: 1, ‘b’: 2}
>>> d4 = d3 # This creates a reference to d3, not a copy
>>> d4[‘a’] = 3 # Mutating a value in d4 also changes d3
>>> d3
{‘a’: 3, ‘b’: 2}
Set Default Values with setdefault()
The Python dictionary setdefault() method is a very useful tool for setting default values in a dictionary. It takes two arguments, the key to be searched for and the value to be returned if the key is not found.
For example, let’s say we have a dictionary of student grades and we want to set a default grade of “C” for any students who are not listed in the dictionary:
grades = {“John”: “A”, “Jane”: “B”, “Jack”: “C”}
grades.setdefault(“John”, “C”)
grades.setdefault(“Jane”, “C”)
grades.setdefault(“Jack”, “C”)
print(grades)
# Output: {‘John’: ‘A’, ‘Jane’: ‘B’, ‘Jack’: ‘C’}
As you can see, the setdefault() method does not change any values that are already in the dictionary. It only sets a default value for keys that are not present.
Get a Specific Value with get()
If you have a key and want to get the corresponding value, use the get() method. The get() method takes two arguments: the key of the value to retrieve and a default value to return if that key does not exist. For example, suppose you have a dictionary named prices that contains key-value pairs like this:
prices = {‘apples’: 0.40, ‘oranges’: 0.35, ‘pears’: 0.50}
If you want to get the value of the ‘oranges’ key, you would use this code:
price = prices.get(‘oranges’)
This would return 0.35. If you tried to get the value of a key that does not exist, like ‘bananas’, you would get None:
price = prices.get(‘bananas’)
print(price) # Prints None
None is not an error; it is just a special value that indicates no value was found. If you want to print an error message when a key is not found, you can provide a default value:
price = prices.get(‘bananas’, ‘Not Found’) # Sets price to ‘Not Found’ if bananas are not in dictionary
print(price)
Update Dictionary Contents with update()
update() is a method that takes another dictionary as an argument and updates the contents of the original dictionary with the key-value pairs from the second dictionary. If a key is in both dictionaries, the value from the second dictionary overwrites the value from the first dictionary. If a key is only in the second dictionary, it’s added to the first dictionary. This method returns None.
Here’s an example:
>>> d1 = {‘a’: 1, ‘b’: 2}
>>> d2 = {‘a’: 3, ‘c’: 4}
>>> d1.update(d2)
>>> print(d1)
{‘a’: 3, ‘b’: 2, ‘c’: 4}
Remove the Last-Added Item with popitem()
The popitem() method returns and removes the last item added to the dictionary. This is useful if you want to process items in the dictionary in reverse order, or if you want to remove a random item from the dictionary.
If you don’t specify a key, popitem() will return and remove the last item added to the dictionary. If you specify a key, it will return and remove the last item with that key.
Remove a Dictionary Item with pop()
If you want to remove a specific key-value pair from a dictionary, you can use the pop() method. The pop() method takes two arguments: the key of the item to remove, and a default value to return if the key is not found. For example, if we have a dictionary named my_dict, we can remove an item with the following code:
my_dict = {‘a’: 1, ‘b’: 2, ‘c’: 3}
# Remove the item with key ‘b’
my_dict.pop(‘b’)
# My dictionary now looks like this:
# {‘a’: 1, ‘c’: 3}
Delete All Dictionary Items with clear()
Python’s dictionary clear() method is used to delete all items from the dictionary. It takes no arguments and returns an empty dictionary.
Example:
>>> my_dict = {‘a’:1, ‘b’:2, ‘c’:3}
>>> my_dict.clear()
>>> my_dict
{}
Conclusion
The Python dictionary is a powerful tool and we have explored just some of the methods available to you. While there are still many more that can be discussed, these 10 methods should provide you with enough knowledge to get started building efficient, robust applications with dictionaries in Python. Make sure to practice your newly acquired skills so that they become second nature before attempting any complex projects. Good luck!
