- Generate A Dictionary With Keys With Empty Sets Python 2
- Dictionary With Keys Python
- Python Initialize Empty Dictionary
Dictionary
Mar 30, 2012 Dictionaries are the fundamental data structure in Python, and a key tool in any Python programmer’s arsenal. They allow O(1) lookup speed, and have been heavily optimized for memory overhead and lookup speed efficiency. Today I”m going to show you three ways of constructing a Python dictionary, as well as some additional tips and tricks. May 20, 2018 In this article we will discuss how to add or append new key value pairs in a dictionary and also how to update value of existing keys. Python dictionary provides a. Mar 11, 2020 In this step-by-step tutorial, you'll learn how the Python defaultdict type works and how to use it for handling missing keys when you're working with dictionaries. You'll also learn how to use a defaultdict to solve problems like grouping or counting the items in a sequence or collection.
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)
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
print(thisdict)
Try it Yourself »
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:
Try it Yourself »There is also a method called
get()
that will give you the same result:Example
Get the value of the 'model' key:
Try it Yourself »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
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict['year'] = 2018
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:
Try it Yourself »Example
Print all values in the dictionary, one by one:
Try it Yourself »Example
You can also use the
Try it Yourself »values()
function to return values of a dictionary:Example
Loop through both keys and values, by using the
Try it Yourself »items()
function: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')
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
if 'model' in thisdict:
print('Yes, 'model' is one of the keys in the thisdict dictionary')
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:
Try it Yourself »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)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict['color'] = 'red'
print(thisdict)
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)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.pop('model')
print(thisdict)
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)
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.popitem()
print(thisdict)
Generate A Dictionary With Keys With Empty Sets Python 2
Try it Yourself »Example
The
del
keyword removes the item with the specified key name: thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
del thisdict['model']
print(thisdict)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
del thisdict['model']
print(thisdict)
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.
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
del thisdict
print(thisdict) #this will cause an error because 'thisdict' no longer exists.
Example
The
clear()
method empties the dictionary: thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.clear()
print(thisdict)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
thisdict.clear()
print(thisdict)
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)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
mydict = thisdict.copy()
print(mydict)
Another way to make a copy is to use the built-in method
dict()
.Example
Make a copy of a dictionary with the
dict()
method: thisdict = {
'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
mydict = dict(thisdict)
print(mydict)
Try it Yourself »'brand': 'Ford',
'model': 'Mustang',
'year': 1964
}
mydict = dict(thisdict)
print(mydict)
Nested Dictionaries
Math worksheet generator and answer key high school. Dragon age product key generator. 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
}
}
Try it Yourself »'child1' : {
'name' : 'Emil',
'year' : 2004
},
'child2' : {
'name' : 'Tobias',
'year' : 2007
},
'child3' : {
'name' : 'Linus',
'year' : 2011
}
}
Or, if you want to nest three dictionaries that already exists as dictionaries:
Example
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
}
Try it Yourself »'name' : 'Emil',
'year' : 2004
}
child2 = {
'name' : 'Tobias',
'year' : 2007
}
child3 = {
'name' : 'Linus',
'year' : 2011
}
myfamily = {
'child1' : child1,
'child2' : child2,
'child3' : child3
}
The dict() Constructor
It is also possible to use the dict() constructor to make a new dictionary:
Dictionary With Keys Python
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)
Try it Yourself »# note that keywords are not string literals
# note the use of equals rather than colon for the assignment
print(thisdict)
Dictionary Methods
Python has a set of built-in methods that you can use on dictionaries.
Python Initialize Empty Dictionary
Method | Description |
---|---|
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 |