Python dictionary key error

Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python KeyError Exceptions and How to Handle Them

Python’s KeyError exception is a common exception encountered by beginners. Knowing why a KeyError can be raised and some solutions to prevent it from stopping your program are essential steps to improving as a Python programmer.

By the end of this tutorial, you’ll know:

• What a Python KeyError usually means
• Where else you might see a KeyError in the standard library
• How to handle a KeyError when you see it

>>> ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
>>> ages['Michael']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'Michael'

 1# ages.py
 2
 3ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
 4person = input('Get age for: ')
 5print(f'{person} is {ages[person]} years old.')

$ python ages.py
Get age for: Michael
Traceback (most recent call last):
File "ages.py", line 4, in <module>
  print(f'{person} is {ages[person]} years old.')
KeyError: 'Michael'

>>> from zipfile import ZipFile
>>> zip_file = ZipFile('the_zip_file.zip')
>>> zip_file.getinfo('something')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/path/to/python/installation/zipfile.py", line 1304, in getinfo
  'There is no item named %r in the archive' % name)
KeyError: "There is no item named 'something' in the archive"

 1# ages.py
 2
 3ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
 4person = input('Get age for: ')
 5age = ages.get(person)
 6
 7if age:
 8    print(f'{person} is {age} years old.')
 9else:
10    print(f"{person}'s age is unknown.")

$ python ages.py
Get age for: Michael
Michael's age is unknown.

age = ages.get(person, 0)

 1# parse_api_response.py
 2...
 3# Assuming you got a `response` from calling an API that might
 4# have an error key in the `response` if something went wrong
 5
 6if 'error' in response:
 7    ...  # Parse the error state
 8else:
 9    ...  # Parse the success state

 1# ages.py
 2
 3ages = {'Jim': 30, 'Pam': 28, 'Kevin': 33}
 4person = input('Get age for: ')
 5
 6try:
 7    print(f'{person} is {ages[person]} years old.')
 8except KeyError:
 9    print(f"{person}'s age is unknown.")

>>> from zipfile import ZipFile
>>> zip = ZipFile('the_zip_file.zip')
>>> try:
...     zip.getinfo('something')
... except KeyError:
...     print('Can not find "something"')
...
Can not find "something"

Watch Now This tutorial has a related video course created by the Real Python team. Watch it together with the written tutorial to deepen your understanding: Python KeyError Exceptions and How to Handle Them

In this Python tutorial, we will study How to solve Python dictionary key errors using some examples in python. Moreover, we will also cover these topics.

• Python dictionary key error handling
• Python dictionary key error but key exists
• Python dictionary key error 0
• Python dictionary key error string
• Python defaultdict key error
• Python dict key error none
• Python dict remove key without error
• Python dictionary try except key error
• Python key error nested dictionary

• In this section, we will discuss what is a key error in the Python dictionary.
• In Python key error is raised when the key does not exist in the dictionary that is used to look up the value.
• For example, suppose you have a dictionary that contains key-value pair within the curly brackets and now if you want to get the particular key from the dictionary which does not exist in the given dictionary then it will raise an error.
• To solve this problem, you can select that item from a dictionary that does exist and you can also handle it by using try-except block.

Example:

my_dict={'U.S.A':15,'France':18,'China':27}

result=my_dict['Japan']
print(result)

In the following given code, we have created a dictionary named ‘my_dict’ that contains elements in the form of key-value pair and then we declared a variable ‘result’ and assign a key element ‘Japan’.

Here is the Screenshot of the following given code.

As you can see in the Screenshot the output displays the keyerror:’japan’ the reason behind this is the key does not exist in the dictionary and it cannot return any value.

Solution

Let’s have a look at the solution to this error by using the get() method

• In Python, the get() method is used to remove the key error and it will check the condition if the key is found then the value is returned, if not then it will raise an error.
• This method is used to retrieve a value from the dictionary and it takes two parameters that indicate the key which we want to be searched and the default value is none.

Syntax:

Here is the Syntax of Python get() method

dict.get(key[,value])

Example:

Let’s take an example and check how to solve this key error

Source Code:

my_dict={'U.S.A':15,'France':18,'China':27}

result=my_dict.get('japan',14)
print("Return value:",result)

Here is the execution of the following given code

As you can see in the Screenshot the output displays the return value is 14.

Also, check: Python Dictionary duplicate keys

Python dictionary key error handling

• In this Program, we will discuss how to solve the key-error problem by using exception handling in Python.
• In Python when your program raises an error or something goes wrong then the try-except method will help the user to catch and handle exceptions.

Example:

Let’s take an example and check how to raise the key error in Python by using handling

my_dictionary = {"George" : 678, "Oliva" : 897, "James" : 156}
  
try:  
  print (my_dictionary["Micheal"])  
except:  
  print ("key error:Key does not contain in dictionary")    

In this example, we have created a dictionary that contains elements in the form of key-value pair and then use the try-except block. This method will check the condition if the key is available in the dictionary then it will display the value of that key and if the key is not available then it will display the message ‘key does not contain in the dictionary’.

Here is the implementation of the following given code.

Solution:

Let’s have a look at the solution to this error

Source Code:

my_dictionary = {"George" : 678, "Oliva" : 897, "James" : 156}

try:  
  print (my_dictionary["Oliva"])  
except:  
  print ("key error:Key does not contain in dictionary")  

In the above code, we have created a dictionary named ‘my_dictionary’ and then we used the handling concept try-except which means if the ‘oliva’ key is available in a dictionary then it will return the value.

Here is the execution of the following given code

As you can see in the Screenshot the output displays the key value that is ‘897‘.

Read: Get First Key in dictionary Python

Python dictionary key error but key exists

• In this section, we will discuss how to solve the key error but key exists in dictionary Python.
• To perform this particular task, first, we will create a dictionary by using curly brackets and the elements are separated by commas.
• To get the key error we are going to use the Python in operator and this operand will check the condition whether a key element is available in the dictionary or not.

Example:

country_name = {'U.S.A':178, 'France':456, 'China':754, 'Australia':345}

 
if 'Germany' in country_name:
    print("Key exist in dictionary")
else:
    print("Key error: Does not contain in dictionary") 

In the above code, we have checked if the ‘Germany’ key exists in a dictionary or not. To do this task first we set the condition if the ‘Germany’ key exists in the dictionary then it will return a value otherwise it will display ‘Key-error’.

Here is the implementation of the following given code.

Read: Python dictionary increment value

Python dictionary key error 0

• In this Program, we will discuss how to solve the key error in the Python dictionary.
• To do this task, we are going to use the indexing method and it is an easy way to get a dictionary key value.
• Let’s take an example and we will see how dictionary indexing works and it will also check whether the key is available in a dictionary or not.

Example:

my_dictionary= {16: 'Germany', 19: 'Japan'} 

print(my_dictionary[0]) 

Here is the execution of the following given code

As you can see in the Screenshot the output displays the key error 0 which means it does not locate the key-value and returns the 0 value.

Let’s have a look at the Solution to this error.

Solution:

my_dictionary= {0: 'Germany', 19: 'Japan'} 

print(my_dictionary[0]) 

In the above code, we have updated the given dictionary ‘my_dictionary’ which means we assigned the key as 0 in the dictionary and set the value ‘Germany’. Once you will execute this code the output displays the ‘Germany’ value.

Here is the Screenshot of the following given code

Read: Python dictionary of lists

Python dictionary key error string

• In this Program, we will discuss how to solve the key error string in the Python dictionary.
• In this example, we are going to use the indexing method to get the key error string.
• To do this task, we will assign the unknown key in the list which is not present in the given dictionary.

Example:

my_dictionary = {'z':178,'y':785,'v':345}

print(my_dictionary['m'])

Here is the Output of the following given code.

As you can see in the screenshot, the output displays the key error which means the key string does not exist in the dictionary.

Solution:

Let’s have a look at the solution to this error.

Example:

my_dictionary = {'z':178,'y':785,'v':345}

print(my_dictionary['y'])

In the above code, we have mentioned the key ‘y’ in the list which is available in the given dictionary. Once you will execute this code it will return the value of that specific key.

Here is the implementation of the following given code.

Read: Python dictionary extend

Python defaultdict key error

In Python defaultdict, it will never generate a key error. Suppose you have a dictionary and now you want to exist a new key by using the default dict method and it takes no arguments, generates a default value for a nonexistent key.

Example:

from collections import defaultdict

my_dict = defaultdict(int)
print(my_dict[4])

Here is the Screenshot of the following given code.

Read: Python dictionary multiple keys

Python dict key error none

• In this section, we will discuss how to get the key error none value in Python dictionary.
• To perform this particular task we are going to use the dict.get() method. In Python, the get() method is used to remove the key error and it will check the condition if the key is found then the value is returned, if not then it will raise an error.

Syntax:

Here is the Syntax of the dictionary.get() method.

dict.get(key[,value])

Example:

my_dict={'a':12,'b':45}

new_result = my_dict.get('c')
print("Key error:",new_result)

Here is the Screenshot of the following given code.

As you can see in the screenshot, the output displays the key error None.

Solution:

my_dict={'a':12,'b':45}

new_result = my_dict.get('a')
print(new_result)

In the following given, code we have created a dictionary named ‘my_dict’ that contains elements in the form of key-value pairs. After that, we used the dict.get() method and assign the key element which is available in the dictionary.

Here is the implementation of the following given code.

As you can see in the screenshot, the output displays the return value of a specific key.

Read: How to create an empty Python dictionary

Python dict remove key without error

• In this Program, we will remove a key from Python dictionary without error.
• To do this task we are going to use the dict.pop() method and it will remove a specific key from dictionary and retuirn its value.
• To get the more information regarding dict.pop() method. You can refer our detail article on Python dictionary pop.

Example:

new_dictionary = {'U.S.A':456,'China':123,'Germany':975}

new_result = new_dictionary.pop('China')
print(new_result)
print("After removing the key:",new_dictionary)

You can refer to the below Screenshot.

As you can see in the Screenshot the output displays the ‘China’ key has been removed from the dictionary.

Read: Python Dictionary to CSV

Python dictionary try except key error

• In this section, we will discuss how to use the try-except block in the Python dictionary and get the key error.
• In Python, try-except block checks the statement if the code does not execute successfully then the program will end at the line and it generates the error while in case of except code will successfully run.
• In this example, we will create a dictionary that contains elements in the form of key-value pair and then we will use the try-except block. This method will check the condition if the key is available in the dictionary then it will display the value of that key
• And if the key is not available then it will display the message ‘key does not contain in the dictionary.

Example:

new_dict = {"U.S.A" : 156, "China" : 2356, "Germany" : 897}
  
try:  
  print (new_dict["Japan"])  
except:  
  print ("key error:Key does not contain in dictionary")  

Here is the Screenshot of the following given code.

Solution:

Let’s have a look at the solution to this error.

Source Code:

new_dict = {"U.S.A" : 156, "China" : 2356, "Germany" : 897}
  
try:  
  print (new_dict["Germany"])  
except:  
  print ("key error:Key does not contain in dictionary")  

Here is the implementation of the following given code

Read: Python dictionary of tuples

Python key error nested dictionary

• Here we are going to discuss how to solve the key error in Python nested dictionary.
• To do this task first we will create a nested dictionary and assign multiple dictionaries. Next, we will use the dict.get() method and this method will help the user to remove the key error and it will check the condition if the key is found then the value is returned, if not then it will raise an error.

Example:

my_dict = { 'Country_name': {'Germany': 678},
                'Desgination': {'Developer': 987}}
new_result = my_dict.get('Number')
print("Key error:",new_result)

In the above code, we have used the dict.get() method and within this function, we have assigned the unknown key element. Once you will execute this code the output displays the key error value ‘None’ which means the key we have assigned in an argument is not present in the given dictionary.

Here is the Screenshot of the following given code.

Solution:

Let’s have a look at the solution to this error.

my_dict = { 'Country_name': {'Germany': 678},
                'Desgination': {'Developer': 987}}
new_result = my_dict.get('Country_name')
print(new_result)

In the above code, we have updated the dict.get() function. In this example, we have assigned the present key which is available in the given dictionary as an argument. Once you will execute this code it will return the value.

You may also like to check the following python tutorials.

• Python dictionary contains + examples
• Python dictionary comprehension
• Python Dictionary Search by value
• Python dictionary initialize
• Python dictionary multiple values
• Python convert dictionary to list

So, in this tutorial, we have learned How to solve Python dictionary key errors using some examples in python. Additionally, we have also covered these topics.

• Python dictionary key error handling
• Python dictionary key error but key exists
• Python dictionary key error 0
• Python dictionary key error string
• Python defaultdict key error
• Python dict key error none
• Python dict remove key without error
• Python dictionary try except key error
• Python key error nested dictionary

The Key Error exception in Python is an exception that most programmers encounter especially when they are getting started with Python dictionaries.

In this article you will learn:

• What does key error mean in Python
• How to fix key errors in Python
• How to handle key errors

What does key error mean?

A Key Error is a way for Python to tell you that you are trying to access a key that doesn’t exist in a dictionary.

Here’s an example, I create a file called keyerror.py…

I define a dictionary that contains countries and their capitals.

First I print the capital of Italy….

…then I print the capital of France.

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}

print(countries['Italy'])
print(countries['France'])

And here’s what I get when I run it:

Rome
Traceback (most recent call last):
  File "keyerror.py", line 3, in <module>
    print(countries['France'])
KeyError: 'France'

As you can see the value related to the first key of the dictionary (Italy) is printed as we want.

But something happens with the second print statement.

A KeyError appears in the output, and that’s because…

Python raises a KeyError when you attempt to access a key that doesn’t exist in a dictionary.

In this case the key ‘France’ doesn’t exist in the countries dictionary.

Notice also how Python can tell at which line of the code the exception has occurred. This is very useful to find the cause of the error quickly when you have hundreds or thousands of lines of code.

Core skill: When Python raises an exception a traceback is included. A traceback is used to give you all the details you need to understand the type of exception and to find what has caused it in your code. 

Makes sense?

How do I fix key errors in Python?

There are two very basic fixes for the key error if your program is simple:

1. Avoid referencing the key that doesn’t exist in the dictionary: this can make sense if, for example, the value of the key has been misspelled. It doesn’t apply to this specific case.
2. Add the missing key to the dictionary: in this case we would add ‘France’ as a key to the dictionary as part of its initial definition.

But those are not robust approaches and don’t prevent a similar error from occurring again in the future.

Let’s look instead at other two options…

First option

Tell Python not to return a KeyError if we try to access a key that doesn’t exist in the dictionary, but to return a default value instead.

Let’s say we want to return the default value ‘Unknown’ for any keys not present in the dictionary…

Here is how we can do it using the dictionary get() method:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}
default = 'Unknown'

print(countries.get('Italy', default))
print(countries.get('France', default))

And the output becomes:

Rome
Unknown

So, at least in this way we have more control over the way our program runs.

Second option

Verify if a key exists in a dictionary using the in operator that returns a boolean (True or False) based on the existence of that key in the dictionary.

In the example below I use the in operator together with an if else Python statement to verify if a key exists before accessing its value:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}

if 'France' in countries:
    print("The capital of France is %" % countries['France'])
else:
    print("The capital of France is unknown")

When I run it I see…

The capital of France is unknown

This is also a good option!

How do you handle key errors?

In the previous section I have introduced the dictionary get() method as a way to return a default value if a key doesn’t exist in our dictionary.

But, what happens if we don’t pass the default value as second argument to the get() method?

Let’s give it a try, being familiar with built-in methods makes a big difference when you write your code:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}

print(countries.get('Italy'))
print(countries.get('France'))

Do you know what the output is?

Rome
None

Interestingly this time Python doesn’t raise a KeyError exception…

…the get() method simply returns None if the key doesn’t exist in the dictionary.

This means that we can implement conditional logic in our code based on the value returned by the get() method. Here’s an example:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}
  
capital = countries.get('France')

if capital:
    print("The capital is %s" % capital)
else:
    print("The capital is unknown")

The output is:

The capital is unknown

A nice way to avoid that ugly exception 🙂

Avoiding the KeyError with a For Loop

Often a way to handle errors is by using programming constructs that prevent those errors from occurring.

I have mentioned before that a KeyError occurs when you try to access a key that doesn’t exist in a dictionary.

So, one way to prevent a KeyError is by making sure you only access keys that exist in the dictionary.

Ok, but how?

You could use a for loop that goes through all the keys of the dictionary…

This would ensure that only keys that are present in the dictionary are used in our code.

Let’s have a look at one example:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}

for key in countries:
    print("The capital of %s is %s" % (key, countries[key]))

And the output is…

The capital of Italy is Rome
The capital of Poland is Warsaw
The capital of UK is London

A for loop can be used to go through all the keys in a dictionary and to make sure you don’t access keys that are not part of the dictionary. This prevents the Python KeyError exception from occurring.

The Generic Approach For Exceptions

Finally, a generic approach you can use with any exceptions is the try except block.

This would prevent Python for raising the KeyError exception and it would allow you to handle the exception in the except block.

This is how you can do it in our example:

countries = {'Italy': 'Rome', 'Poland': 'Warsaw', 'UK': 'London'}
  
try:
    print('The capital of France is %s' % countries['France'])
except KeyError:
    print('The capital of France is unknown')

As you can see, in this case, the except block is written specifically to handle the KeyError exception.

In this case we could have also used a generic exception (removing KeyError)…

try:
    print('The capital of France is %s' % countries['France'])
except:
    print('The capital of France is unknown')

So, do we really need to specify the exception type?

It can be very handy if the try code block could raise multiple types of exceptions and we want to handle each type differently.

Conclusion

Now you have a pretty good idea on how to handle the KeyError exception in Python.

Few options are available to you, choose the one you prefer…

Are you gonna use the get() method or the in operator?

Do you prefer the try except approach?

Let me know in the comments below 🙂

Are you getting started with Python?

I have created a checklist for you to quickly learn the basics of Python. You can download it here for free.

Before we dive into KeyError in Python, it is important to know how a dictionary in python is set up. The following pointers will be discussed in this article:

• Dictionary in Python
• KeyError in Python
• Handling Mechanism for a KeyError
• A Generic Solution

Dictionary in Python

The dictionary concept in Python is a random collection of values, which has stored data values like a map. It is unlike other data types that hold only a single value as an element. It holds the key: value pair.

The key value makes it more efficient. A colon separates a key and value pair and a ‘comma’ separates each key. This dictionary in python functions similar to a normal dictionary. The respective keys should be unique and of immutable data types such as strings, integers, and tuples, but the key-values can be iterated and is allowed to be of any type. There can be keys, which are strings that refer to numbers and vice versa.

Let us have a look at how a dictionary functions through the below-coded example.

# Creating an empty Dictionary 
Dict = {} 
print("Null dict: ") 
print(Dict) 

# Creating Dictionary with Integer Keys 
Dict = {1: 'Fun', 2: 'And', 3: 'Frolic'} 
print("nDictionary with the use of Integer Keys: ") 
print(Dict) 

# Creating Dictionary with Mixed keys 
Dict = {'Name': 'Arun', 1: [12, 23, 34, 45]} 
print("nDictionary with the use of Mixed Keys: ") 
print(Dict) 

# Creating a Dictionary with dict() method 
Dict = dict({1: 'German', 2: 'language', 3:'is fun'}) 
print("nDictionary with the use of dict(): ") 
print(Dict) 

# A Dictionary having each item as a Pair 
Dict = dict([(1, 'Hello'), (2, 'Bye')]) 
print("nDictionary with each item as a pair: ") 
print(Dict)

KeyError in Python

Since we are clear on what a dictionary in python is and how it works. Now let us see what a key error is. KeyError in Python is raised when you attempt to access a key that is not in a dictionary.

The mapping logic is a data structure that maps one set of data to significant others. Hence, it is an error, which is raised when the mapping is accessed and not found. It is familiar to a lookup error where the semantic bug would be stated as the key you are looking for is not to be found in its memory. This can be better illustrated in the below code.

Here I am trying to access a key called “D” which is not present in the dictionary. Hence, the error is thrown as soon as it finds an exception. However, the remaining keys present in the dictionary, which are printed correctly, have the exact values corresponding to them. 

// 
ages={'A':30,'B':28,'C':33}
print(ages['A'])
print(ages['B'])
print(ages['C'])
print(ages['D'])
//

Handling Mechanism for a KeyError in Python

Anyone who encounters a KeyError can handle it in a responsible way. It is his skill to consider all possible inputs to a certain program and handle any precarious entries successfully.

Depending on your use case, some of these solutions might be better or may also not be the exact solution what you are looking for. Nevertheless, the ultimate goal is to stop unexpected key error exceptions from popping up.

If an error is brought from a dictionary in your own code, you can use .get() to extract either the value at the specified key or a default value. Let us have a look at a sample.

//List of fruits and their prices. 

while(1):
fruits= {'Apple': 300, 'Papaya': 128, 'Kiwi': 233}
fruit= input('Get price for: ')
fruit1 = fruits.get(fruit)
if fruit1:
    print(f'{fruit} is {fruit1} rupees.')
else:
    print(f"{fruit}'s cost is unknown.")

A Generic Solution to KeyError

The usual solution is that you can always use the try-except block to tackle such problems by raising the appropriate code and provide a backup solution. Check out the below code for more clarity.

//
while(1):
 ages = {'Jophi': 12, 'Rao': 20, 'Irvin': 16} 
 person = input('Get age for: ')

 try:
    print(f'{person} is {ages[person]} years old.')
 except KeyError:
    print(f"{person}'s age is unknown.")
//

With this, we come to an end of this KeyError in Python article. I hope this article was informative in throwing light on Python’s KeyError exception and how it could be raised. Also, you may be aware now that in case the problem is a dictionary key lookup in your own code, then you can switch from accessing the key directly on the dictionary to using the .get() method with a default return value.

If the problem is not coming from your own code, then using the try-except block for better controlling your code’s flow.

To get in-depth knowledge of Python along with its various applications, you can enroll now for live Python course training with 24/7 support and lifetime access.

Got a question for us? Mention them in the comments section of “KeyError in Python” and we will get back to you.

Отображение – это структура данных в Python, которая отображает один набор в другом наборе значений. Словарь Python является наиболее широко используемым для отображения. Каждому значению назначается ключ, который можно использовать для просмотра значения. Ошибка ключа возникает, когда ключ не существует в сопоставлении, которое используется для поиска значения.

В этой статье мы собираемся обсудить ошибки keyerror в Python и их обработку с примерами. Но прежде чем обсуждать ошибку ключа Python, мы узнаем о словаре.

Словарь (dict) в Python – это дискретный набор значений, содержащий сохраненные значения данных, эквивалентные карте. Он отличается от других типов данных тем, что имеет только один элемент, который является единственным значением. Он содержит пару ключей и значений. Это более эффективно из-за ключевого значения.

Двоеточие обозначает разделение пары ключа и значения, а запятая обозначает разделение каждого ключа. Этот словарь Python работает так же, как и обычный словарь. Ключи должны быть уникальными и состоять из неизменяемых типов данных, включая строки, целые числа и кортежи.

Давайте рассмотрим пример, чтобы понять, как мы можем использовать словарь (dict) в Python:

 
# A null Dictionary  
Dict = {}  
print("Null dict: ")  
print(Dict)  
  
# A Dictionary using Integers  
Dict = {1: 'Hill', 2: 'And', 3: 'Mountin'}  
print("nDictionary with the use of Integers: ")  
print(Dict)  
  
# A Dictionary using Mixed keys  
Dict = {'Name': 'John', 1: [17, 43, 22, 51]}  
print("nDictionary with the use of Mixed Keys: ")  
print(Dict)  
  
# A Dictionary using the dict() method  
Dict = dict({1: 'London', 2: 'America', 3:'France'})  
print("nDictionary with the use of dict(): ")  
print(Dict)  
  
# A Dictionary having each item as a Pair  
Dict = dict([(1, 'Hello'),(2, 'World')])  
print("nDictionary with each item as a pair: ")  
print(Dict) 

Вывод:

Null dict:  
{} 
nDictionary with the use of Integers:  
{1: 'Hill', 2: 'And', 3: 'Mountin'} 
nDictionary with the use of Mixed Keys:  
{'Name': 'John', 1: [17, 43, 22, 51]} 
nDictionary with the use of dict():  
{1: 'London', 2: 'America', 3: 'France'} 
nDictionary with each item as a pair:  
{1: 'Hello', 2: 'World'} 

Keyerror в Python

Когда мы пытаемся получить доступ к ключу из несуществующего dict, Python вызывает ошибку Keyerror. Это встроенный класс исключений, созданный несколькими модулями, которые взаимодействуют с dicts или объектами, содержащими пары ключ-значение.

Теперь мы знаем, что такое словарь Python и как он работает. Давайте посмотрим, что определяет Keyerror. Python вызывает Keyerror всякий раз, когда мы хотим получить доступ к ключу, которого нет в словаре Python.

Логика сопоставления – это структура данных, которая связывает один фрагмент данных с другими важными данными. В результате, когда к сопоставлению обращаются, но не находят, возникает ошибка. Это похоже на ошибку поиска, где семантическая ошибка заключается в том, что искомого ключа нет в его памяти.

Давайте рассмотрим пример, чтобы понять, как мы можем увидеть Keyerror в Python. Берем ключи A, B, C и D, у которых D нет в словаре Python. Хотя оставшиеся ключи, присутствующие в словаре, показывают вывод правильно, а D показывает ошибку ключа.

 
# Check the Keyerror 
ages={'A':45,'B':51,'C':67} 
print(ages['A']) 
print(ages['B']) 
print(ages['C']) 
print(ages['D']) 

Вывод:

45 
51 
67 
Traceback(most recent call last): 
File "", line 6, in  
KeyError: 'D' 

Механизм обработки ключевой ошибки в Python

Любой, кто сталкивается с ошибкой Keyerror, может с ней справиться. Он может проверять все возможные входные данные для конкретной программы и правильно управлять любыми рискованными входами. Когда мы получаем KeyError, есть несколько обычных методов борьбы с ним. Кроме того, некоторые методы могут использоваться для обработки механизма ошибки ключа.

Обычное решение: метод .get()

Некоторые из этих вариантов могут быть лучше или не могут быть точным решением, которое мы ищем, в зависимости от нашего варианта использования. Однако наша конечная цель – предотвратить возникновение неожиданных исключений из ключевых ошибок.

Например, если мы получаем ошибку из словаря в нашем собственном коде, мы можем использовать метод .get() для получения либо указанного ключа, либо значения по умолчанию.

Давайте рассмотрим пример, чтобы понять, как мы можем обработать механизм ошибки ключа в Python:

 
# List of vehicles and their prices.  
vehicles = {"Car=": 300000, "Byke": 115000, "Bus": 250000} 
vehicle = input("Get price for: ") 
vehicle1 = vehicles.get(vehicle) 
if vehicle1: 
    print("{vehicle} is {vehicle1} rupees.") 
else: 
    print("{vehicle}'s cost is unknown.") 

Вывод:

Get price for: Car 
Car is 300000 rupees. 

Общее решение для keyerror: метод try-except

Общий подход заключается в использовании блока try-except для решения таких проблем путем создания соответствующего кода и предоставления решения для резервного копирования.

Давайте рассмотрим пример, чтобы понять, как мы можем применить общее решение для keyerror:

 
# Creating a dictionary to store items and prices 
items = {"Pen" : "12", "Book" : "45", "Pencil" : "10"} 
try: 
  print(items["Book"]) 
except: 
  print("The items does not contain a record for this key.")   

Вывод:

45 

Здесь мы видим, что мы получаем стоимость книги из предметов. Следовательно, если мы хотим напечатать любую другую пару «ключ-значение», которой нет в элементах, она напечатает этот вывод.

 
# Creating a dictionary to store items and prices 
items = {"Pen" : "12", "Book" : "45", "Pencil" : "10"} 
try: 
  print(items["Notebook"]) 
except: 
  print("The items does not contain a record for this key.")  

Вывод:

The items does not contain a record for this key. 

Заключение

Теперь мы понимаем некоторые распространенные сценарии, в которых может быть выброшено исключение Python Keyerror, а также несколько отличных стратегий для предотвращения их завершения нашей программы.

В следующий раз, когда мы столкнемся с ошибкой Keyerror, мы будем знать, что это, скорее всего, связано с ошибочным поиском ключа словаря. Посмотрев на последние несколько строк трассировки, мы можем получить всю информацию, которая нам понадобится, чтобы выяснить, откуда взялась проблема.

Если проблема заключается в поиске ключа словаря в нашем собственном коде, мы можем использовать более безопасную функцию .get() с возвращаемым значением по умолчанию вместо запроса ключа непосредственно в словаре. Если наш код не вызывает проблемы, блок try-except – лучший вариант для регулирования потока нашего кода.

Исключения не должны пугать. Мы можем использовать эти методы, чтобы наши программы выполнялись более предсказуемо, если мы понимаем информацию, представленную нам в их обратных трассировках, и первопричину ошибки.