What is Python Dictionary?
A python dictionary consists of keys and values. It is helpful to compare a dictionary to a list. Instead of the numerical indexes such as a list, dictionaries have keys. These keys are the keys that are used to access values within a dictionary.
It is very simple to create a dictionary as placing items inside {} separated by , commas.
Each item will have a KEY and a corresponding VALUE consecutively, it will look like {Key:Value}.
While the values can be of any data type and can repeat, keys must be of immutable type and must be unique.
In [59]:
# This is example of Dictonary
Dict = {"A" : 1, "B" : 2, "Key3" : 3, "Key4" : 4}
Dict
Out[59]:
{'A': 1, 'B': 2, 'Key3': 3, 'Key4': 4}
In [76]:
#Access Dictionary Values Dict ["A"]
Out[76]:
1
Dict [(0,1)]
Each key is separated from its value by a colon “:”. Commas separate the items, and the whole dictionary is enclosed in curly braces. An empty python dictionary without any items is written with just two curly braces, like this “{}”.
In [86]:
# Create a sample dictionary
Name_Age_Dict = {"Umair": "1985", "Simmi": "1980", \
"Moon": "1973", "Sumaira": "1992", \
"Ali": "1977", "Asghar": "1976", \
"Tahira": "1977", "Fatima": "1977"}
Name_Age_Dict
#capital letter effects the results.
Out[86]:
{'Umair': '1985',
'Simmi': '1980',
'Moon': '1973',
'Sumaira': '1992',
'Ali': '1977',
'Asghar': '1976',
'Tahira': '1977',
'Fatima': '1977'}
In [87]:
# Get value by key Name_Age_Dict['Tahira']
Out[87]:
'1977'
In [88]:
# Get all the keys in dictionary Name_Age_Dict.keys()
Out[88]:
dict_keys(['Umair', 'Simmi', 'Moon', 'Sumaira', 'Ali', 'Asghar', 'Tahira', 'Fatima'])
In [89]:
# Get all the values in dictionary Name_Age_Dict.values()
Out[89]:
dict_values(['1985', '1980', '1973', '1992', '1977', '1976', '1977', '1977'])
In [91]:
# Append value with key into dictionary Name_Age_Dict ['Tahira'] = '1992' Name_Age_Dict
Out[91]:
{'Umair': '1985',
'Simmi': '1980',
'Moon': '1973',
'Sumaira': '1992',
'Ali': '1977',
'Asghar': '1976',
'Tahira': '1992',
'Fatima': '1977',
'Graduation': '2007'}
In [92]:
# Delete entries by key del(Name_Age_Dict['Ali']) Name_Age_Dict
Out[92]:
{'Umair': '1985',
'Simmi': '1980',
'Moon': '1973',
'Sumaira': '1992',
'Asghar': '1976',
'Tahira': '1992',
'Fatima': '1977',
'Graduation': '2007'}
In [93]:
#verify 'Ali' in Name_Age_Dict
Out[93]:
False
In [94]:
#verify 'Umair' in Name_Age_Dict
Out[94]:
True
In [13]:
V={'A','B'}
V.add('C')
V
Out[13]:
{'A', 'B', 'C'}
In [19]:
A = {'1','2'}
a=set(A)
a
Out[19]:
{'1', '2'}
In [20]:
type(set([1,2,3]))
Out[20]:
set
In [21]:
{'a','b'} &{'a'}
Out[21]:
{'a'}
Python Dictionary Methods
Methods that are available with a dictionary are tabulated below. Some of them have already been used in the above examples.
| Method | Description |
|---|---|
| clear() | Removes all items from the dictionary. |
| copy() | Returns a shallow copy of the dictionary. |
| fromkeys(seq[, v]) | Returns a new dictionary with keys from seq and value equal to v (defaults to None). |
| get(key[,d]) | Returns the value of the key. If the key does not exist, returns d (defaults to None). |
| items() | Return a new object of the dictionary’s items in (key, value) format. |
| keys() | Returns a new object of the dictionary’s keys. |
| pop(key[,d]) | Removes the item with the key and returns its value or d if key is not found. If d is not provided and the key is not found, it raises KeyError. |
| popitem() | Removes and returns an arbitrary item (key, value). Raises KeyError if the dictionary is empty. |
| setdefault(key[,d]) | Returns the corresponding value if the key is in the dictionary. If not, inserts the key with a value of d and returns d (defaults to None). |
| update([other]) | Updates the dictionary with the key/value pairs from other, overwriting existing keys. |
| values() | Returns a new object of the dictionary’s values |
