This article will discuss four methods for checking if a list within a dictionary is empty. Before that, let’s briefly review how to access items in the Python dictionary as a prerequisite.

Accessing Elements of a Python Dictionary

Items of a Python dictionary can be accessed using the dictionary keys. This can be done using the square brackets or <dict>.get(<key>) function as shown below.

# Define a dictionary with three keys.
data1 = {
    "schools": ["Braeburn", "Zetech", "TUB", "Yale", "Warsaw"],
    "teachers": [],
    "other_info": {"fees": [3450, 2800, 4680, 6200, 5100], "cities": []},
}
# Example 1: Access the values of the "schools" key
schools = data1["schools"]
print(schools)
schools = data1.get("schools")
print(schools)
# Example 2: Accessing values for nested dictionary.
fees = data1["other_info"]["fees"]
print(fees)
fees = data1.get("other_info").get("fees")
print(fees)

Output:

['Braeburn', 'Zetech', 'TUB', 'Yale', 'Warsaw']
['Braeburn', 'Zetech', 'TUB', 'Yale', 'Warsaw']
[3450, 2800, 4680, 6200, 5100]
[3450, 2800, 4680, 6200, 5100]

The main difference between the two methods: using <dict>[<key>] raises an error if the key being accessed does not exist, but <dict>.get(<key>) will return None.

Checking If the List within a Dictionary is Empty

This Section covers four methods for this purpose.

Method 1: Using if-statement

An empty list in Python is considered falsy. That means “if <list>” returns False if <list> is empty; otherwise, it returns True. Let’s see an example.

data1 = {
    "schools": ["Braeburn", "Zetech", "TUB", "Yale", "Warsaw"],
    "teachers": [],
    "other_info": {"fees": [3450, 2800, 4680, 6200, 5100], "cities": []},
}
# not <list> returns True if <list> is empty.
if not data1["teachers"]:
    print("The list is empty.")
else:
    print("The list is not empty.")

Output:

The list is empty.

Method 2: Using the bool() function

The bool(<obj>) evaluates the object passed to it as either True or False. If an empty list is passed, bool(<obj>) evaluates to False; otherwise, it evaluates to True. For example,

data1 = {
    "schools": ["Braeburn", "Zetech", "TUB", "Yale", "Warsaw"],
    "teachers": [],
    "other_info": {"fees": [3450, 2800, 4680, 6200, 5100], "cities": []},
}
print("Check if empty (False if empty): ", bool(data1["other_info"]["fees"]))
print("Check if empty (true if not empty): ", bool(data1["teachers"]))

Output:

Check if empty (False if empty):  True
Check if empty (true if not empty):  False

Method 3: By checking its length

The length of a list can be determined using the inbuilt len() function. If the size of a list is zero, then it is effectively an empty list; otherwise, the length of the list is equal to the number of elements in it. For example,

lst1 = ["Ammon", 45, "Still"]
print(len(lst1)) # 3
lst2 = []
print(len(lst2)) # 0

With that in mind, we can now check if a list within a dictionary is empty using len() and if-statement, as shown below.

data1 = {
    "schools": ["Braeburn", "Zetech", "TUB", "Yale", "Warsaw"],
    "teachers": [],
    "other_info": {"fees": [3450, 2800, 4680, 6200, 5100], "cities": []},
}
if len(data1["schools"]) > 0:
    print("List is not empty.")
else:
    print("List is empty.")
if len(data1["other_info"]["cities"]) > 0:
    print("The list is not empty.")
else:
    print("The list is empty.")

Output:

The list is not empty.
The list is empty.

Method 4: By comparing it to an empty list

We can also check if a list is empty by comparing it with a truly empty list using the comparison operator (==). If the list (say A) being checked is empty, then A==[ ] will return True; otherwise, it will return False.

data1 = {
    "schools": ["Braeburn", "Zetech", "TUB", "Yale", "Warsaw"],
    "teachers": [],
    "other_info": {"fees": [3450, 2800, 4680, 6200, 5100], "cities": []},
}
if data1["schools"] == []:
    print("List is not empty.")
else:
    print("List is empty.")
if data1["other_info"]["cities"] == []:
    print("List is not empty.")
else:
    print("List is empty.")

Output:

The list is empty.
The list is not empty.

Conclusion

In this post, we learned four approaches to checking if a list within a dictionary is empty. The methods discussed include: using if-statement, checking the length of the list, using the bool() method, and comparing the list in question with an empty list.