Dictionary: dictionary (dict) python is the only type of a map he is enclosed in {} key is unique to the composition in dict when saving the key, key calculated according to a memory address.... the key-value is then stored in the address. such an algorithm is called a hash algorithm, therefore, remember, the key is stored in the dict key-value must be a hash, while in a dictionary unique key . Hash currently available data types: int, str, tuple, bool. Not hash data types: list, dict, set.
Syntax: {key1: value1, key2: value2 ....} Note: The key-value pair is disordered, so that the operation can not be sliced.
1. increase
dict [key] = value if the key does not exist, a new key-value pair; if key is present, it will replace the corresponding value.
dict.setdefault (key, value) if the key does not exist, add a key-value pair; if the key exists, setdefault not work.
2. deleted
dict.pop (key) to delete the specified key-value, and returns the corresponding value
del dict [key] to delete the specified key-value
dict.popitem () random delete key-value, while the return key-value.
dict.clear () to empty the contents of the dictionary
3. change
dict [existing key] = new value,
d1.update (d2) the contents d2 d1 is updated to the more. If the same name key. Alternatively the modification. If key does not exist, is new.
4. Charles
dict [key] can direct the investigation, if the key does not exist error.
dict.get (key) to check directly, if the key does not exist, returns None, or dict.get (key, return value), the set return value.
dict.setdefault (key, value) if the key does not exist, adding a key-value pair, and returns the corresponding value; if key is present, the return value inherent.
5. Other related operations
dict.keys () to obtain all the dictionary key, then there is a high copy list may be used for loop through
dict.values () to obtain all the dictionary value, then there is a high copy list
dict.items () Gets all key-value pairs to the dictionary, and then a list exists in the form of imitation tuple
More convenient a, b = [1, 2] cycle through other tuples; deconstruction \ unpack a, b = 1, 2; a, b = (1, 2)
6. nesting dictionary
eg：dic1 = {
"name": "小明",
"age": 28,
"wife": {
"name": '小红',
"age": 28
},
"children": ['第⼀个毛孩', '第⼆个⽑孩'],
}
print(dic1.get("wife").get("name"))
print(dic1.get("children"))
print(dic1.get("children")[1])
7 difference between == and is the
== comparison value is equal on both sides of the variable
is the memory address of the variable is equal on both sides of the comparison Note: The address query variable print (id (variable))
Supplement is used when the address:
# Numeric data pool range -5 to 256, when the numbers within this range, the address is equal on both sides of IS
# If there are special characters in the string of their memory address is not the same
# * String as a single memory address them within 20, 21 or more inconsistent single memory address *
NOTE: The only difference between the two can be compared only when the terminal performs out, PyCharm not, all of the same file, a py strings are generally used as the memory address.
The coding and decoding
encode (encoding) ---- get the corresponding encoded bytes of plaintext
decode (decoding method) ----- The encoded bytes decoded to the plain text
Note: What is necessary to encode what is decoded, otherwise it will be garbled.
supplement:
python3 in running stage using Unicode, you can display all content. pycharm when stored default utf-8 type.
Data transfer and storage type bytes are used.
Coding knowledge:
ASCII code:
does not support Chinese
support alphanumeric symbols
8 byte
gbk code GB:
supports Chinese, English, numbers, symbols
English 16 two-byte
Chinese 16 two-byte
unicode Unicode
support for Chinese, English, numbers, symbols,
English four-byte 32-bit
Chinese four 32-bit byte
utf-8 Unicode variable length with a minimum 8
English 8 byte
Chinese three bytes 24