Also keep in mind that popitem removes the key-value pair from dictionary, as stated in the docs. How do I generate random integers within a specific range in Java? How to get the current time in Python. How do I sort a dictionary by value? Jun 30, 2018  Now we want to create a dictionary with all elements in this list as keys. For each key value will be same i.e. Let’s see how to do that i.e. A normal dictionary performs a simple mapping of a key to a value. This recipe shows two easy, efficient ways to achieve a mapping of each key to multiple values. The semantics of the two approaches differ slightly but importantly in how they deal with duplication. Apr 11, 2020 Let see how to use the random.choice function to select random key-value pair from a Python dictionary. The random.choice function of a random module doesn’t accept a dictionary, you need to convert a dictionary into a list before passing it to randonm.choice function. Let see the example of how to choose dict keys randomly.

Dictionary

A dictionary is a collection which is unordered, changeable and indexed. In Python dictionaries are written with curly brackets, and they have keys and values.

Example

Create and print a dictionary:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
print(thisdict)
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Accessing Items

You can access the items of a dictionary by referring to its key name, inside square brackets:

Example

Get the value of the 'model' key:

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There is also a method called get() that will give you the same result:

Example

Get the value of the 'model' key:

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Change Values

You can change the value of a specific item by referring to its key name:

Example

Change the 'year' to 2018:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict['year'] = 2018
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Loop Through a Dictionary

You can loop through a dictionary by using a for loop.

When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

Example

Print all key names in the dictionary, one by one:

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Example

Print all values in the dictionary, one by one:

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Example

You can also use the values() function to return values of a dictionary:

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Example

Loop through both keys and values, by using the items() function:

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Check if Key Exists

To determine if a specified key is present in a dictionary use the in keyword:

Example

Check if 'model' is present in the dictionary:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
if 'model' in thisdict:
print('Yes, 'model' is one of the keys in the thisdict dictionary')
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Dictionary Length

To determine how many items (key-value pairs) a dictionary has, use the len() method.

Example

Print the number of items in the dictionary:

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Adding Items

Adding an item to the dictionary is done by using a new index key and assigning a value to it:

Example

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict['color'] = 'red'
print(thisdict)
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Removing Items

There are several methods to remove items from a dictionary:

Example

The pop() method removes the item with the specified key name:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.pop('model')
print(thisdict)
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Example

The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead):

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.popitem()
print(thisdict)
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Example

The del keyword removes the item with the specified key name:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
del thisdict['model']
print(thisdict)
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Example

The del keyword can also delete the dictionary completely:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
del thisdict
print(thisdict) #this will cause an error because 'thisdict' no longer exists.

Generating A Dictoary With Key From A Set Lyrics

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Example

The clear() method empties the dictionary:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.clear()
print(thisdict)
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Copy a Dictionary

You cannot copy a dictionary simply by typing dict2 = dict1, because: dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.

There are ways to make a copy, one way is to use the built-in Dictionary method copy().

Example

Make a copy of a dictionary with the copy() method:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
mydict = thisdict.copy()
print(mydict)
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Another way to make a copy is to use the built-in method dict().

Example

Generating A Dictoary With Key From A Set

Make a copy of a dictionary with the dict() method:

thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
mydict = dict(thisdict)
print(mydict)
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Nested Dictionaries

A dictionary can also contain many dictionaries, this is called nested dictionaries.

Example

Create a dictionary that contain three dictionaries:

myfamily = {
'child1' : {
'name' : 'Emil',
'year' : 2004
},
'child2' : {
'name' : 'Tobias',
'year' : 2007
},
'child3' : {
'name' : 'Linus',
'year' : 2011
}
}
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Or, if you want to nest three dictionaries that already exists as dictionaries:

Example

Generating A Dictionary With Key From A Settlement

Create three dictionaries, than create one dictionary that will contain the other three dictionaries:

child1 = {
'name' : 'Emil',
'year' : 2004
}
child2 = {
'name' : 'Tobias',
'year' : 2007
}
child3 = {
'name' : 'Linus',
'year' : 2011
}
myfamily = {
'child1' : child1,
'child2' : child2,
'child3' : child3
}
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The dict() Constructor

It is also possible to use the dict() constructor to make a new dictionary:

Example

thisdict = dict(brand='Ford', model='Mustang', year=1964)
# note that keywords are not string literals
# note the use of equals rather than colon for the assignment
print(thisdict)
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Dictionary Methods

Python has a set of built-in methods that you can use on dictionaries.

MethodDescription
clear()Removes all the elements from the dictionary
copy()Returns a copy of the dictionary
fromkeys()Returns a dictionary with the specified keys and value
get()Returns the value of the specified key
items()Returns a list containing a tuple for each key value pair
keys()Returns a list containing the dictionary's keys
pop()Removes the element with the specified key
popitem()Removes the last inserted key-value pair
setdefault()Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update()Updates the dictionary with the specified key-value pairs
values()Returns a list of all the values in the dictionary
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Description

Python dictionary method fromkeys() creates a new dictionary with keys from seq and values set to value.

Syntax

Following is the syntax for fromkeys() method −

Parameters

  • seq − This is the list of values which would be used for dictionary keys preparation.

  • value − This is optional, if provided then value would be set to this value

Return Value

This method returns the list.

Example

The following example shows the usage of fromkeys() method.

When we run above program, it produces following result −

python_dictionary.htm
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