How to Get Python Dictionary Keys by Value Question

Getting the key of a Python dictionary by value

The python dictionary operation of getting values with the keys of a key-value pair is still relatively simple.

Example:

d = {1:'a', 2:'a', 3:'b', 5:'c'}
print(d[5])

The output result is:

c

However, since values are not unique in the dictionary, looking up the key corresponding to a value is quite laborious. Here is a function that looks up the key from the value, resulting in a list of keys corresponding to the input value:

def get_keys_by_value(the_dict, the_value):
	rl = list()
	for k in the_dict.keys():
		if the_dict[k] == the_value:
			(k)
	return rl
if __name__ == "__main__":
	d = {1:'a', 2:'a', 3:'b', 8:'f'}
	print('the keys are: ', get_keys_by_value(d, 'a'))

The first parameter (the_dict) of the function get_keys_by_value is the dictionary object on which the function operates, the second parameter (the_value) is the value to be queried, and the return parameter is the corresponding key, and the type of the return value is a list since there may be more than one corresponding key.

The result of the run is:

======================== RESTART: C:/Users/luh/ ========================
the keys are:  [1, 2]
>>> 

We generally use this function when we need to find a key by value in programming.

Several ways to fetch values from python dictionaries

A Python dictionary (dictionary) is a mutable container model that can store any number of data of any type. Each element of a dictionary consists of a key and a value, separated by a colon. Dictionaries are typically used to store data in key-value pairs, such as records in a database.

Here are a few methods of Python dictionary fetching and their code demonstrations:

Method 1: Use square bracket [ ] operators

Use the square bracket [ ] operator to get the corresponding value in the dictionary by key.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Get the value of the "name" key in the dictionary.
value = my_dict["name"]
print(value)  # exports：Tom

Method 2: Use the get() method

Use the get() method to get the corresponding value in the dictionary by key, or return None if the key does not exist.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Get the value of the "name" key in the dictionary.
value = my_dict.get("name")
print(value)  # Output: Tom
# Get the value of the key "phone" in the dictionary, returns None since "phone" does not exist.
value = my_dict.get("phone")
print(value)  # exports：None

Method 3: Use the items() method

Use the items() method to get all the key-value pairs in the dictionary, returning a list containing all the key-value pairs, where each element in the list is a tuple, the first element of the tuple is the key, and the second element is the value.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Get all key-value pairs in the dictionary
items = my_dict.items()
print(items)  # Output: dict_items([('name', 'Tom'), ('age', 18), ('gender', 'male')])
# Iterate over all key-value pairs
for key, value in items:
    print(f"{key}: {value}")

Method 4: Use the keys() method

Use the keys() method to get all the keys in the dictionary, returning a list of all the keys.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Get all keys in the dictionary
keys = my_dict.keys()
print(keys)  # Output: dict_keys(['name', 'age', 'gender'])
# Iterate over all keys
for key in keys:
    value = my_dict[key]
    print(f"{key}: {value}")

Method 5: Using the values() method

Use the values() method to get all the values in the dictionary, returning a list of all the values.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Get all values in the dictionary
values = my_dict.values()
print(values)  # Output: dict_values(['tom', 18, 'male'])
# Iterate over all values
for value in values:
    print

Method 6: Use of the in keyword

Use the in keyword to determine whether a key is in the dictionary, returning True if it is and False otherwise.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Determine if "name" is in the dictionary #
if "name" in my_dict:
    print("name is in my_dict")  # Output: name is in my_dict
# Determine if "phone" is in the dictionary.
if "phone" in my_dict:
    print("phone is in my_dict")
else:
    print("phone is not in my_dict")  # exports：phone is not in my_dict

Method 7: Using the pop() method

Use the pop() method to remove the key-value pair for the specified key in the dictionary and return the corresponding value.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Delete the key-value pair for the "age" key in the dictionary and return the corresponding value
value = my_dict.pop("age")
print(value)  # Output: 18
print(my_dict)  # exports：{"name": "Tom", "gender": "male"}

Method 8: Using the popitem() method

Using the popitem() method you can delete any key-value pair in the dictionary and return the corresponding key-value pair, which is returned as a tuple where the first element of the tuple is the key and the second element is the value.

# Define a dictionary
my_dict = {"name": "Tom", "age": 18, "gender": "male"}
# Delete any key-value pair in the dictionary and return the corresponding key-value pair
key, value = my_dict.popitem()
print(key, value)  # Output: gender male
print(my_dict)  # exports：{"name": "Tom", "age": 18}　

This is a demonstration of several methods of Python dictionary fetching and their code.

ultimate

The above is a personal experience, I hope it can give you a reference, and I hope you can support me more.