1. Definition of dictionary
Format of the dictionary: dictionary name = {key1:value1, key2:value2,...}
Dictionaries are unordered and are variable data types
The key of a dictionary cannot be a mutable data type (list dictionary)
Dictionary keys cannot be duplicated, but values can be
Example: my_dict = {"name": "Xiaoming", "age": 19}
Define an empty dictionary: my_dict = {} or my_dict = dict()
2. Common operations of the dictionary
Define a dictionary
my_dict = {"name": "Little Ming.", "age": 18, "no": "007"}
(1) View element (get value by key)
value = my_dict["no"] print(value)
(2) Modifying elements
If the key exists, then the value corresponding to the key is modified.
If the key does not exist, then the key-value pair is added to the dictionary.
# key exists my_dict["age"] = 19 print(my_dict) # key does not exist my_dict["test"] = "Testing." print(my_dict)
Related recommendation: "Python Tutorial
(3) Deletion of elements
del deletes the specified element Format: del dictionary name [key] deletes the element (key-value)
del my_dict["name"] print(my_dict)
clear() clears all elements of the dictionary.
my_dict.clear()
# Equivalent to {}
print(my_dict)
(4) Calculate the number of elements len()
l = len(my_dict) print(l)
(5) Returns a list of all keys of the dictionary keys()
keys_list = my_dict.keys() print(list(keys_list))
(6) Returns a list of all values of the dictionary values()
values_list = my_dict.values() print(list(values_list))
(7) return a list of all (key, value) tuples items()
items_list = my_dict.items() print(list(items_list))
(8) Determine whether the key exists
in exists not in does not exist
if "name" in my_dict:
print("Name exists.")
（9）setdefault
If my_dict.setdefault(key)
If the key exists, get the value.
If the key doesn't exist, you get None, not found.
value = my_dict.setdefault("name")
print(value)
If my_dict.setdefault(key, value1) value1 Default value
If the key exists, get the value.
If the key doesn't exist, the resulting value1 is added to the dictionary as a new key-value pair.
value = my_dict.setdefault("name1", "Ha ha.")
print(value)
print(my_dict)
（10）get
my_dict.get(key)
If key exists, get value.
If the key doesn't exist, you get None, not found.
ret = my_dict.get("gender")
print(ret)
my_dict.get(key, value1)
If the key exists, get the value.
If the key doesn't exist, you get value1. You don't do anything with the dictionary.
ret = my_dict.get("name1", "Ha ha.")
print(ret)
print(my_dict)
3. Iteration of the dictionary
Define a dictionary
my_dict = {"name": "Old King.", "age": 22, "no": "009"}
(1) Iterate over the key
for key in my_dict.keys(): print(key)
(2) Iterate over value
for value in my_dict.values(): print(value)
(3) Iterate over items
for item in my_dict.items(): print(item)
(4) Iterate over items to get the corresponding key value
for key, value in my_dict.items(): print(key, value)
(5) enumerate () implementation with subscript index traversal
Iterate over strings, lists, and tuples to get the corresponding elements and their subscript indexes.
my_list = ["fgg", "rth", "rkz"] for index, value in enumerate(my_list): print(index, value)
Results:
fgg rth rkz
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