Python Dictionary Introduction

Pythondictionary (Dictionary)

A dictionary is another mutable container model and can store any type of object.

Each key value of the dictionary (Key=>value) is split with a colon (:), each pair is separated by a comma (,), and the entire dictionary is enclosed in curly braces ({}) , as shown in the following format:

D = {key1 : value1, key2 : value2 }< /c13>

The key must be unique, but the value does not have to be.

The value can take any data type, but the key must be immutable, such as a string, a number, or a tuple.

A simple Dictionary instance:

Dict = {'Alice': '2341', ' Beth ' : ' 9102 ' , ' Cecil ' : ' 3258 ' }

You can also create a dictionary like this:

Dict1 = { 'abc': 456 }; Dict2 = { 'abc': 123, 98.6: PNs };

Accessing values in the dictionary

Put the corresponding key into the familiar square brackets, the following example:

In [161]: a = {"name": "Zpy", "Age": "All"}in [162]: aout[162]: {' age ': ' + ', ' name ': ' Zpy '}in [163]: a[' name ']out[163]: ' Zpy '

Modify Dictionary

The way to add new content to a dictionary is to add a new key/value pair, modify or delete an existing key/value pair as follows:

In [165]: a["age"]= 11In [166]: aout[166]: {' age ': one, ' name ': ' Zpy '}

Add Key-vauel Dictionary

In [167]: a["sex"]= "woman" in [168]: aout[168]: {' age ': one, ' name ': ' zpy ', ' sex ': ' Woman '}

Delete a dictionary element

The ability to delete a single element also clears the dictionary, emptying only one operation.

Show Delete a dictionary with the Del command, as in the following example:

In [a[]: del ' name '] #删除名字key-vaulein [171]: aout[171]: {' age ': one, ' sex ': ' Woman '}in [172]: A.clear () #清空字典In [173 ]: aout[173]: {}in [174]: del a # #删除字典In [175]: A---------------------------------------------------------------------------nameerror Trac  Eback (most recent) <ipython-input-175-60b725f10c9c> in <module> ()----> 1 Anameerror:name ' a ' is Not defined

Properties of Dictionary Keys

A dictionary value can take any Python object without restriction, either as a standard object or as a user-defined one, but not a key.

Two important points to keep in mind:

1) The same key is not allowed to appear two times. When created, if the same key is assigned a value of two times, the latter value is remembered, as in the following example:

In [176]: Dict = {' name ': ' Zara ', ' age ': 7, ' name ': ' Manni '};in [177]: Print dict[' name ']manni

2) The key must be immutable, so it can be used as a number, a string, or a tuple, so you can't use a list.

Dictionary built-in functions & methods

The Python dictionary contains the following built-in functions:

Serial Number	Functions and descriptions
1	CMP (Dict1, DICT2) Compares two dictionary elements.
2	Len (dict) Calculates the number of dictionary elements, that is, the total number of keys.
3	STR (DICT) The output dictionary is a printable string representation.
4	Type (variable) Returns the type of the variable entered and returns the dictionary type if the variable is a dictionary.

The Python dictionary contains the following built-in methods:

Serial Number	Functions and descriptions
1	Dict.clear () Delete all elements in a dictionary
2	Dict.copy () Returns a shallow copy of a dictionary
3	Dict.fromkeys (seq[, Val])) Create a new dictionary with the keys to the dictionary in sequence seq, Val is the initial value corresponding to all keys in the dictionary
4	Dict.get (Key, Default=none) Returns the value of the specified key if the value does not return the default value in the dictionary
5	Dict.has_key (Key) Returns False if the key returns true in the dictionary Dict
6	Dict.items () Returns an array of traversed (key, value) tuples as a list
7	Dict.keys () Returns a dictionary of all keys in a list
8	Dict.setdefault (Key, Default=none) Similar to get (), but if the key does not exist in the dictionary, the key is added and the value is set to default
9	Dict.update (DICT2) Update the key/value pairs of the dictionary dict2 to the Dict
10	Dict.values () Returns all values in the dictionary as a list
11	Pop (Key[,default]) Deletes the value of the dictionary given key key, and returns the value to be deleted. The key value must be given. Otherwise, the default value is returned.
12	Popitem () Randomly returns and deletes a pair of keys and values in the dictionary.

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Python Dictionary Introduction