This is the second day of my participation in the August Text Challenge.More challenges in August


Dictionary definition

  • dict(Dictionary) yesApart from the list PythonAmong theThe most flexibleData type of
  • Dictionaries can also be usedStoring multiple data
    • Usually used to store relevant information describing an object
  • And a list
    • A list is an ordered collection of objects
    • A dictionary is an unordered collection of objects
  • Dictionary use{}Define ordict()
  • Dictionary useKey/value pairStore data, used between key-value pairs.separated
    • key keyIs the index
    • value valueIs the data
    • key 和 valueUsed between:separated
    • The key has to be unique
    • Values can take any data type, but keys can only be strings, numbers, or tuples


xiaoming = {
    "name": "Xiao Ming"."age": 18."gender": True."height": 1.75
}
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Common dictionary operations

  • inIPythonTo define aThe dictionary, such as:goods_dict= {}
  • The inputgoods_dict.Press theTABThe key,IPythonYou will be promptedThe dictionaryThe following methods can be used:


The usefulness of each method is illustrated in the figure above, so here are a few common methods/operations to test.

A dictionary definition

In [81] :Empty dictionary definition

In [82]: goods_dict = {}

In [83]: goods_dict2 = dict()

In [84] :type(goods_dict)
Out[84] :dict

In [85] :type(goods_dict2)
Out[85] :dict
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In [86] :# dictionary definitions with data
                                       ^
In [88]: goods_dict ={'name': 'Nuggets T-shirt'.'price': 59}

In [89]: goods_dict2 = dict(name='Nuggets T-shirt', price=59)

In [90] :type(goods_dict), type(goods_dict2)
Out[90] : (dict.dict)

In [91]: goods_dict
Out[91] : {'name': 'Nuggets T-shirt'.'price': 59}

In [92]: goods_dict2
Out[92] : {'name': 'Nuggets T-shirt'.'price': 59}
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Dictionary add data

In [94]: goods_dict
Out[94] : {'name': 'Nuggets T-shirt'.'price': 59}

In [95] :# add data
In [96]: goods_dict['size'] = 'L'

In [97]: goods_dict
Out[97] : {'name': 'Nuggets T-shirt'.'price': 59.'size': 'L'}
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Dictionary delete data

In [102]: goods_dict
Out[102] : {'name': 'Nuggets T-shirt'.'price': 59.'size': 'L'}

In [103] :Delete key data

In [104] :del goods_dict['size']

In [105]: goods_dict
Out[105] : {'name': 'Nuggets T-shirt'.'price': 59}

In [106]: goods_dict.pop('price')
Out[106] :59

In [107]: goods_dict
Out[107] : {'name': 'Nuggets T-shirt'}

In [108]: goods_dict.popitem()
Out[108] : ('name'.'Nuggets T-shirt')

In [109]: goods_dict
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Del goods_dict[key] and goods_dict.pop(key) are both specified keys. Delete key-value pairs in the dictionary.

  • delThere is no return value,pop()Returns the value of the current delete keyvalue

Goods_dict.popitem () randomly deletes a dictionary key-value pair and returns the deleted key-value pair.



In [111]: goods_dict
Out[111] : {'name': 'Nuggets T-shirt'.'price': 59}

In [112] :Empty the dictionary data

In [113]: goods_dict.clear()

In [114]: goods_dict
Out[114] : {}Copy the code


Dictionary update data

In [116]: goods_dict
Out[116] : {'name': 'Nuggets T-shirt'.'price': 59}

In [117] :Update dictionary data

In [118]: goods_dict['name'] = 'Gold Digger badge'

In [121]: goods_dict
Out[121] : {'name': 'Gold Digger badge'.'price': 59}

In [122]: goods_dict.setdefault('price'.18)
Out[122] :59

In [123]: goods_dict
Out[123] : {'name': 'Gold Digger badge'.'price': 59}

In [124]: goods_dict.setdefault('size'.'M')
Out[124] :'M'

In [125]: goods_dict
Out[125] : {'name': 'Gold Digger badge'.'price': 59.'size': 'M'}
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The setdefault() method in the dictionary does not update the key value when the corresponding key already exists in the dictionary, but can only be used to increase the key-value pair. The dictionary [key] is updated if the key exists, and added if it does not exist.


In [127]: goods_dict
Out[127] : {'name': 'Gold Digger badge'.'price': 59.'size': 'M'}

In [128] :# Overall update

In [130]: new_info = {'price': 18.'size': '5cm'}

In [131]: goods_dict.update(new_info)

In [132]: goods_dict
Out[132] : {'name': 'Gold Digger badge'.'price': 18.'size': '5cm'}

In [133]: new_info = {'name': 'Gold Digger Booklet XX'.'author': 'hui'.'price': 19.9}

In [134]: goods_dict.update(new_info)

In [135]: goods_dict
Out[135] : {'name': 'Gold Digger Booklet XX'.'price': 19.9.'size': '5cm'.'author': 'hui'}
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The update(new dictionary) method in a dictionary merges the new dictionary into the original dictionary. If the key is the same, it will be updated. If the key is not, it will be added.


The dictionary gets the value of the specified key

In [137]: goods_dict
Out[137] : {'name': 'Gold Digger Booklet XX'.'price': 19.9.'size': '5cm'.'author': 'hui'}

In [138] :Get the value of the specified key

In [139]: goods_dict['name']
Out[139] :'Gold Digger Booklet XX'

In [140]: goods_dict['author']
Out[140] :'hui'

In [141]: goods_dict.get('price')
Out[141] :19.9

In [142]: goods_dict['id'] --------------------------------------------------------------------------- KeyError Traceback (most recent call last)  <ipython-input-142-b8a93fe9ad6b> in <module>
----> 1 goods_dict['id']

KeyError: 'id'

In [145]: ret = goods_dict.get('id')

In [147] :print(ret)
None

In [148]: count = goods_dict.get('count'.0)

In [149]: count
Out[149] :0
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Get (key), which defaults to None if the key does not exist. You can change the default return value, such as goods_dict.get(‘count’, 0), which defaults to 0 if the key does not exist.


other

In [154]: goods_dict
Out[154] : {'name': 'Gold Digger Booklet XX'.'price': 19.9.'author': 'hui'}

In [155] :# The number of key-value pairs in the dictionary

In [156] :len(goods_dict)
Out[156] :3

In [157] :Get all keys in the dictionary

In [158]: goods_dict.keys()
Out[158]: dict_keys(['name'.'price'.'author'])

In [161] :Get all values in the dictionary

In [162]: goods_dict.values()
Out[162]: dict_values(['Gold Digger Booklet XX'.19.9.'hui'])

In [163] :# all key-value pairs in the dictionary (tuple list)

In [164]: goods_dict.items()
Out[164]: dict_items([('name'.'Gold Digger Booklet XX'), ('price'.19.9), ('author'.'hui')])
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Dictionary loop through

  • Traversal is to get all the key-value pairs in turn from the dictionary

In [167] :for key ingoods_dict: ... :print('key', key) ... :print('value', goods_dict[key]) ... :print(a)... :... : Key name value xx Key Price value19.9

key author
value hui
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for … in … By default, all keys in the dictionary keys() are taken, and then values are obtained by keys.

However, we can iterate through the keys and values once through items() in the dictionary

In [168] :for key, value ingoods_dict.items(): ... :print(key, value) ... :print(a)... :... : Name Gold nuggets booklet XX Price19.9

author hui
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Application scenarios

  • Although it can be usedfor intraverseThe dictionary
  • However, in development, more application scenarios are:
    • Use multiple key-value pairs to store information that describes an object — more complex data information
    • Put multiple dictionaries in a list and iterate, doing the same for each dictionary inside the body of the loop
info_list = [
    {
        "name": "hui"."qq": "222815"."phone": "10010"
    },
             
    {
        "name": "zack"."qq": "54321"."phone": "10086"
    },
    
    {
        "name": "wang"."qq": "12345"."phone": "10000"}]Copy the code


The tail language

✍ Code writes the world and makes life more interesting. ❤ ️

✍ thousands of rivers and mountains always love, ✍ go again. ❤ ️

✍ code word is not easy, but also hope you heroes support. ❤ ️