Dictionary manipulation in Python
Dictionary manipulation
Mutable Data type
syntax: d = {key:value}, d = dict(), d = {}
Duplicates Key not allowed
Duplicates Values allowed
Heterogeneous values are allowed for both k,v
No array means no indexing
Insertion order not maintained
d = dict()
print(type(d))
d = {}
print(type(d))
d = {"a":"Apple","b":"Ball"}
print(d)
d = {"a":"Apple",2:"Ball",3:[4,7,(3,6)]}
print(d)
Accessing Elements from dictionary
1. using [key_name]
if we try to access key_name that is not present in dic then it throws keyerror.
2. using get(key_name)
if we try to access key_name that doesn't exist in dic then it does not throw any error.
print(d["a"])
print(d.get("a"))
print(d.get("c"))
#print(d["c"]) #keyerror
Update And Add elements from Dictionary
using Assignment operator we are able to add or change the element. If the key is present then value will be updated otherwise new element is added with key:value.
d["a"] = "Amazon"
print(d)
d["c"] = "Cat"
print(d)
Remove the Key
1. pop(key)
Used to remove the provided key from the dictionary and return the value.
If key not available and you try to remove it throw keyerror
It return data type is based on value.
2.popitem()
Used to remove the arbitrary element and return the removed key and value as a tuple data type.
It return tuple data type.
3. clear()
Used to remove all elements from dictionary
It return none
4. del dict_name
Used to remove the dictionary. Removed from memory as well
print(d.pop("c"))
#print(d.pop("c"))#if key not available
print(d.popitem())
print(d.clear())
print(d)
del d
#print(d)
fromkeys(), keys() and items(), update()
fromkeys(sequence,value)
It creates a new dictionary with a given sequence of elements with a value provided by the user if value is not present then value is set as a none.
seq = {'1','2','3','4'}
print(type(seq))
print(dict.fromkeys(seq,'number'))
print(dict.fromkeys(seq))
#mutable object issue
val = ["num1"]
dict1 = dict.fromkeys(seq,val)
print(dict1)
val.append("num2")
print(dict1)
This happens because each element is assigned a reference to the same object (points to the same object in the memory).
To avoid this issue, we use dictionary comprehension.
2.keys()
this method returns all keys from given dictionary.
If we get all keys from dictionary and saved in one variable and after that we add one key in dictionary that time variable data also get changed
numKeys = dict1.keys()
print(numKeys)
#after update
dict1.update({'5':"num2"})
print(numKeys)
print(dict1)
3.items()
The items() method returns a view object that displays a list of dictionary's (key, value) tuple pairs.
numItems = dict1.items()
print(numItems)
#after update
dict1.update({'6':"num2"})
print(numItems)
setdefault(key,value(optional))
This method returns the value of a key if the key is in the dictionary. If not, it inserts a key with a value if the value is not assigned then sets none.
default1 = dict1.setdefault("6")
print(default1)
#if Not withoutvalue
default1 = dict1.setdefault("8")
print(default1)
#if Not withvalue
default1 = dict1.setdefault("9",'num1')
print(default1)
