Python: Dictionary
What is Dictionary
A python “dictionary” is a ordered list of pairs, each is a key and a value. (It also known as “keyed list”, “associative array”, “hash table”, in other languages.)
Before Python 3.7 (May 2018), dictionary is unordered.
Create Dictionary
{key1:val1, key2:val2, etc}
hh = {"john":3, "mary":4, "joe":5} print(hh) # {'joe': 5, 'john': 3, 'mary': 4}
Add a Entry
dict[key] = value
hh = {"john":3, "mary":4} # add a entry hh["vicky"] = 99 print(hh) # {'john': 3, 'mary': 4, 'vicky': 99}
Delete a Entry
del dict[key]
hh = {"a":3, "b":4, "c":5} # delete a entry del hh["b"] print(hh) # {'a': 3, 'c': 5}
Check Key Exist
key in dict
hh = {"a":3, "b":4, "c":5} # check if a key exists print("b" in hh) # True
Get Key's Value
dict[key]
hh = {"john":3, "mary":4, "joe":5} print(hh["mary"]) # 4
Get Count
hh = {"a":3, "b":4, "c":5} print(len(hh) )
Get All Keys
dict.keys()
hh = {"a":3, "b":4, "c":5} print(hh.keys()) # dict_keys(['a', 'b', 'c']) print(list(hh.keys())) # ['a', 'b', 'c']
Get All Values
dict.values()
hh = {"a":3, "b":4, "c":5} # get all values print(hh.values()) # dict_values([3, 4, 5])
What Type Can be Used as Key in Dictionary?
A key in dictionary can be anything that's hashable. Basically, string, tuple, number, or in general python data types that are “immutable”.
# dict key can be anything that's hashable. typically, number, string, tuple. Most things that are “immutable” hh = {2:3, "b":4, (3,4):5} print(2 in hh) # True print((3,4) in hh) # True
~2012 Thanks to 孙翰菲 for a tip.
Python, Data Structure
- Python: List
- Python: Generate List: range
- Python: List Comprehension
- Python: List Methods
- Python: Iterate List
- Python: Map f to List
- Python: Filter List
- Python: Iterator to List
- Python: Copy Nested List, Shallow/Deep Copy
- Python: Interweave Lists to Tuples, Transpose
- Python: Sort
- Python: Convert List to Dictionary
- Python: Dictionary
- Python: Iterate Dictionary
- Python: Dictionary Methods
- Python: Tuple
- Python: Sets, Union, Intersection
- Python: Sequence Types
- Python: Read Write JSON