- Python Program to Search an Element in a Dictionary
- How to Search an Element From a Dictionary?
- Using “for” and “in” Loop
- Example
- Output
- Using items + list
- Example
- Output
- Using dict.item()
- Example
- Output
- Using list.index()
- Example
- Output
- Conclusion
- Python: Check if a Key (or Value) Exists in a Dictionary (5 Easy Ways)
- What is a Python Dictionary?
- The Problem with Indexing a Python Dictionary
- Use Python to Check if a Key Exists: Python keys Method
- Use Python to Check if a Key Exists: Python in Operator
- Use the .get Method to Check if a Key Exists in a Python Dictionary
- Check if a Value Exists in a Python Dictionary Using .values()
Python Program to Search an Element in a Dictionary
Dictionaries are used to store data values in key:value pairs like maps (which unlike other data types holds only a single value as an element). key:value is provided in dictionaries to make it more effective. Keys are unique. Dictionary key must be unique. So, no duplicate values are allowed in dictionaries. Dictionaries items are ordered, changeable, immutable. Changeable means here is that, we can add or remove items after the dictionaries are created.
In this article, we will know about how to search an element in dictionary by using different functions. There are many functions to search an element in dictionary by using different method like “for” and “in”, list.index(), dict.item(), by using item+list etc.
How to Search an Element From a Dictionary?
Here, we have given a dictionary of numbers and we have to search an element from a dictionary by using different methods. There four methods to search an element in a dictionary.
- By using “for” and “in” loop
- By Using items() + list
- By using dict.item()
- By using list.index()
Using “for” and “in” Loop
A for loop is used to execute a statement repeatedly until given condition is satisfied. And when condition becomes false, the line immediately after the loop in the program is executed.
The “in” operator determines whether a given value is constituent element of a sequence such as a string, array, list, or tuple, dictionary. It is used to search an element in a dictionary. For example −
Example
Here, we have a program in which we have used “for loop” for searching an element in a dictionary. In this program we have searched “value=3” element that exists in a dictionary. So, output comes as “cherry”.
fruit = print("The original dictionary is : " + str(fruit)) val = 3 for key in fruit: if fruitPython find element in dict == val: res = key print("The key corresponding to value : " + str(res))
Output
The original dictionary is : The key corresponding to value : cherry
Using items + list
List is a data structure in python, which is changeable, mutable and iterable ordered sequence of element. They are used to store multiple elements in a single variable. List allows duplicate elements.
By using the items(), which is used to extract both keys and values at once, hence making the search easy and can be executed using list makes process of searching a elements in a dictionary easy.
Example
Here, we have a program in which we have used “item()+list” for searching an element in a list. In this program, we have searched “value=2” element that exists in a dictionary. So, output comes as ”mango”.
fruit = print("The original dictionary is : " + str(fruit)) val = 2 res = Python find element in dict print("The key corresponding to value : " + str(res))
Output
The original dictionary is : The key corresponding to value : ['mango']
Using dict.item()
By using the dict.items(), which is used to extract both keys and values from a value by matching all the values.
Example
Here, we have a program in which we have used “dict.item()” to searching an element in a list. In this program we have searched “100 and 11” element that exists in a dictionary. So, output comes as ”java and C”.
def get_key(val): for key, value in program.items(): if val == value: return key return "key doesn't exist" program = print(get_key(100)) print(get_key(11))
Output
Using list.index()
This is one liner code for searching an element in a dictionary by using indentation.
Example
Here, we have a program in which we have used “list.index()” for searching an element in a dictionary. In this program, we have search index “112” element that exists in a dictionary. So, output comes as ”python”.
program = print("One line Code Key value: ", list(program.keys()) [list(program.values()).index(112)])
Output
One line Code Key value: Python
Conclusion
In this article, we have briefly discussed about the different methods used to search an element in a dictionary.
Python: Check if a Key (or Value) Exists in a Dictionary (5 Easy Ways)
In this tutorial, you’ll learn how to use Python to check if a key exists in a dictionary. You’ll also learn how to check if a value exists in a dictionary. You’ll learn how to do this using the in operator, the .get() method, the has_key() function, and the .keys() and .values() methods.
Knowing how to work with Python dictionaries is an important skill. This can be especially helpful when working with web APIs that return JSON data.
While we can easily index a dictionary, if a key doesn’t exist, a KeyError will be thrown. This will cause some significant problems in your program, unless these errors are handled.
A much more safe alternative to using dictionary indexing, is to first check if a given key exists in a dictionary. Let’s get started learning!
The Quick Answer: Use in to see if a key exists
What is a Python Dictionary?
Dictionaries in Python are one of the main, built-in data structures. They consist of key:value pairs that make finding an items value easy, if you know their corresponding key. One of the unique attributes of a dictionary is that keys must be unique, but that values can be duplicated.
Let’s take a look at how dictionaries look in Python. They’re created using <> curly brackets and the key:value pairs are separated by commas.
Let’s create a dictionary called ages , which, well, contains the ages of different people:
One way that you’re often taught to access a dictionary value is to use indexing via the [] square bracket accessing. In the next section, you’ll see how dictionary indexing works and why it’s not always the best option. Following that, you’ll learn different methods of ensuring that a key exists.
The Problem with Indexing a Python Dictionary
Indexing a dictionary is an easy way of getting a dictionary key’s value – if the given key exists in the dictionary. Let’s take a look at how dictionary indexing works. We’ll use dictionary indexing to get the value for the key Nik from our dictionary ages :
We can see here that this worked beautifully. That being said, let’s see if we try to get the value for the key Jill , which doesn’t exist in the dictionary:
>>> ages = >>> print(ages['Jill']) KeyError: 'Jill'
We can see here, that if we try to access a dictionary’s value for a key that doesn’t exist, that a KeyError is thrown. This has some huge implications for your code. Unless the error is explicitly handled, the program will fail. One way to avoid a KeyError is to ensure that a key actually exists in a Python dictionary.
That’s exactly what you’ll learn in the next few sections. Let’s get started!
Use Python to Check if a Key Exists: Python keys Method
Python dictionary come with a built-in method that allows us to generate a list-like object that contains all the keys in a dictionary. Conveniently, this is named the .keys() method.
Printing out dict.keys() looks like this:
print(ages.keys()) # Returns: dict_keys(['Matt', 'Katie', 'Nik', 'Jack', 'Alison', 'Kevin'])
We can see how that looks like a little bit like a list. We can now check if a key exists in that list-like object!
Let’s see how we can use the .keys() method to see if a key exists in a dictionary. Let’s use this method to see if a key exists:
# Check if a key exists in a Python dictionary by checking all keys ages = some_key = 'James' if some_key in ages.keys(): print('Key exists') else: print('Key doesn\'t exist') # Returns Key doesn't exist
We can see here that we check whether or not a provided key, some_key , exists in the keys of our dictionary. In this case, the key didn’t exist and the program printed out Key doesn’t exist .
In the next section, you’ll learn how to simplify this even further!
Use Python to Check if a Key Exists: Python in Operator
The method above works well, but we can simplify checking if a given key exists in a Python dictionary even further. We can actually omit the .keys() method entirely, and using the in operator will scan all keys in a dictionary.
Let’s see how this works in practise:
ages = some_key = 'Nik' if some_key in ages: print('Key exists') else: print('Key doesn\'t exist') # Returns: Key exists
We can see here that our method actually looks very similar to the above, but we’ve been able to strip out the .keys() method entirely! This actually helps the code read a bit more plain-language.
in the next section, you’ll learn how to actually retrieve a key’s value, even if a key doesn’t exist!
Use the .get Method to Check if a Key Exists in a Python Dictionary
Working with dictionaries in Python generally involves getting a key’s value – not just checking if it exists. You learned earlier that simply indexing the dictionary will throw a KeyError if a key doesn’t exist. How can we do this safely, without breaking out program?
The answer to this, is to use the Python .get() method. The .get() method will simply return None if a key doesn’t exist. Let’s try this out:
ages = print(ages.get('Jack')) print(ages.get('Jill')) # Returns: # 43 # None
We can see here that when the .get() method is applied to return a key that exists, that key’s value is correctly returned. When a key doesn’t exist, the program continues to run, but it returns None .
What is particularly helpful about the Python .get() method, is that it allows us to return a value, even if a key doesn’t exist.
Say we wanted our program to notify us that a key didn’t exist. We could ask the .get() method to return “Key doesn’t exist!”.
Let’s see how we can do this:
ages = print(ages.get('Jill', "The key doesn't exist")) # Returns: "The key doesn't exist!"
The .get() method is a great and safe way to see if a key exists in a Python dictionary. Now, let’s learn to see whether or not a given value exists in a Python dictionary.
Check if a Value Exists in a Python Dictionary Using .values()
Similar to the Python dictionary .keys() method, dictionaries have a corresponding .values() method, which returns a list-like object for all the values in a dictionary.
Let’s see how we can access all of a dictionary’s values:
ages = print(ages.values()) #Returns: dict_values([30, 29, 31, 43, 32, 38])
We can use this to see whether or not a value exists. Say we wanted to know if the age 27 existed in our dictionary, we could write the following:
ages = some_age = 27 if some_age in ages.values(): print('Age exists!') else: print("Age doesn't exist!") # Returns: Age doesn't exist!
Now, what if we wanted to return the key or keys for a given value. We can safely do this using a list comprehension, which will have three permutations:
- Be an empty list, if the value doesn’t exist,
- Have one item, if the value exists once
- Have more than one item, if the value exists more than once
Let’s use a slightly modified dictionary to see this in action:
# Getting all keys of a certain value in a Python dictionary ages = value_43 = Python find element in dict print(value_43) # Returns: ['Jack', 'Jill']
We’ve created a list comprehension that adds each key, if the value of that key is equal to 43.
What are Python List Comprehensions? To learn more about list comprehensions, check out my comprehensive tutorial here and my in-depth video below!