聊一聊:Python 字典 的用法(二)

恋习Python

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2019-12-01 23:21

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作者:刘帅

博文地址:https://www.cnblogs.com/liu-shuai/


聊一聊:Python 字典 的用法


字典是Python语言中唯一的映射类型。字典对象是可变的,它是一个容器类型,支持异构、任意嵌套。


has_key


  功能:判断字典中是否存在指定键

  语法:D.has_key(k) -> True if D has a key k, else False

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'}2 >>>D.has_key('n4')3 False4 ######################################################5 >>>D.has_key('n2')6 True


items


  功能:返回以字典中的键值对组成的元组作为元素的列表

  语法:D.items() ->  list of D's (key, value) pairs, as 2-tuples

  实例展示:

>>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'}2 >>>L = D.items()3 >>>print L4 [('n1', 'liushuai'), ('n2', 'spirit'), ('n3', 'tester')]5 >>>type(L)6 'list'>


iteritems


  功能:对以字典中的键值对组成的元组进行迭代,可用于for循环

  语法:D.iteritems() -> an iterator over the (key, value) items of D

  实例展示:

>>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>L = D.iteritems() 3 >>>print L 4 0x7faea6c97158>  #生成一个迭代器地址 5 >>>L.next()              #开始迭代 6 ('n1', 'liushuai') 7 >>>L.next() 8 ('n2', 'spirit') 9 >>>L.next()10 ('n3', 'tester')11 >>>L.next()              #迭代完成后报错12 Traceback (most recent call last):13   File "", line 1, in <module>14 StopIteration15 #########################################################################16 >>>for i in D.iteritems():      #使用for循环遍历17 ...    print i18 ...19 ('n1', 'liushuai')20 ('n2', 'spirit')21 ('n3', 'tester')


iterkeys


  功能:对字典中的键进行迭代(遍历)

  语法:D.iterkeys() -> an iterator over the keys of D

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>L = D.itervalues() 3 >>>print L 4 0x7faea6c971b0> 5 >>>L.next()                 6 'n1' 7 >>>L.next() 8 'n2' 9 >>>L.next()10 'n3'11 >>>L.next()12 Traceback (most recent call last):13   File "", line 1, in <module>14 StopIteration15 #############################################################16 >>>for i in D.iterkeys():17 ...     print i18 ...19 n120 n221 n3


itervalues


  功能:对字典中的键进行迭代(遍历)

  语法:D.itervalues() -> an iterator over the values of D

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>L = D.itervalues() 3 >>>print L 4 0x7faea6c97208> 5 >>>L.next()               6 'liushuai' 7 >>>L.next() 8 'spirit' 9 >>>L.next()10 'tester'11 >>>L.next()12 Traceback (most recent call last):13   File "", line 1, in <module>14 StopIteration15 #############################################################16 >>>for i in D.itervalues():17 ...     print i18 ...19 liushuai20 spirit21 tester


keys


  功能:以列表的形式返回所有键

  语法:D.keys() -> list of D's keys

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'}2 >>>L = D.keys()3 >>>print L4 ['n1','n2','n3']


pop


  功能:从字典中删除指定的键,返回其对应的值。

  语法:D.pop(k[,d]) -> v, remove specified key and return the corresponding value. If key is not found, d is returned if given, otherwise KeyError is raised

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>D.pop('n4')        #指定的键不存在,返回报错 3 Traceback (most recent call last): 4   File "", line 1, in <module> 5 ################################################## 6 KeyError: 'n4'        #指定的键不存在,返回指定的值 7 >>>D.pop('n4','check') 8 'check' 9 ##################################################10 >>>D.pop('n2')            #指定的键存在,返回其对应值11 'spirit'12 ##################################################13 >>>D.pop('n3','check')    #指定的键存在,指定值无效,依然返回其对应值14 'tester'15 ##################################################


popitem


  功能:随机删除字典的键值对并以元组的形式返回

  语法:D.popitem() -> (k, v), remove and return some (key, value) pair as a
    2-tuple; but raise KeyError if D is empty.

  实例展示:

>>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>D.popitem() 3 ('n1', 'liushuai') 4 >>>D.popitem() 5 ('n2', 'spirit') 6 >>>D.popitem() 7 ('n3', 'tester') 8 >>>D.popitem()             #当字典为空时,抛出异常。 Traceback (most recent call last):     File "", line 1, in <module>   KeyError: 'popitem(): dictionary is empty'


setdefault


  功能:查找键值。若键不在字典中,将会添加键并将值设定为默认值

  语法:D.setdefault(k[,d]) -> D.get(k,d), also set D[k]=d if k not in D

  实例展示:

>>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 ##指定的键存在,则返回其对应的值,原字典不变 3 >>>D.setdefault('n2') 4 'spirit' 5 >>>print D 6 {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 7 ####################################################################### 8 ##指定的键不存在,则修改原字典,该键对应的值默认为none 9 >>>D.setdefault('n4')10 >>>print D11 {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester', 'n4': None}12 #######################################################################13 ##指定的键不存在,则修改原字典,该键对应的值为指定值14 >>>D.setdefault('n5','check')15 >>>print D16 {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester', 'n4': None, 'n5': 'check'}


update


  功能:以字典或迭代器更新原字典

  语法:D.update([E, ]**F) -> None.  Update D from dict/iterable E and F.
        If E present and has a .keys() method, does:     for k in E: D[k] = E[k]
        If E present and lacks .keys() method, does:     for (k, v) in E: D[k] = v
        In either case, this is followed by: for k in F: D[k] = F[k]

  实例展示:

>>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'} 2 >>>D1 = {'n1':'liush','n4':'Jerry'} 3 >>>D2 = {1:'IT',2:'SALE'} 4 #键相同时,则其对应的原字典的值将被覆盖 5 >>>D.update(D1) 6 {'n1': 'liush', 'n2': 'spirit', 'n3': 'tester', 'n4': 'Jerry'} 7 #################################################### 8 #键不同时,则追加 9 >>>D.update(D2)10 {1: 'IT', 2: 'SALE', 'n1': 'liush', 'n2': 'spirit', 'n3': 'tester', 'n4': 'Jerry'}


values


  功能:以列表的形式返回所有值

  语法:D.values() -> list of D's values

  实例展示:

 >>>D = {'n1': 'liushuai', 'n2': 'spirit', 'n3': 'tester'}2 >>>L = D.values()3 >>>print L4 ['liushuai', 'spirit', 'tester']

已完!


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