Python入门第11课——循环初步（只读课堂）

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In [1]: #欢迎来到“只读课堂”！往期课程和Python资料包请找QQ：1649643021，我们的学习交流群：206527832
In [2]: #下面我们来讲讲循环
In [3]: #循环有：for 循环 - 遍历循环， while 循环 - 条件循环
In [4]: costs = [3,4,12,23,43,100]
In [5]: #如果我要把这个清单整理好，要用“花费。。。花费。。。”打印出来：
In [6]: for cost in costs:   ...: print('消费{}元'format(cost)) File "<ipython-input-6-c06e3a352828>", line 2 print('消费{}元'format(cost)) ^SyntaxError: invalid syntax

In [7]: #上面少了个点
In [8]: for cost in costs:   ...: print('消费{}元'.format(cost))   ...: 消费3元消费4元消费12元消费23元消费43元消费100元
In [9]: #它就，可以很完整地展示
In [10]: #可以再规整点儿：
In [11]: for cost in costs:    ...: print('消费{}元'.format(str(cost).center(10)))    ...: 消费 3 元消费 4 元消费 12 元消费 23 元消费 43 元消费 100 元
In [12]: #————————————————————————————————————————————————————————————————
In [13]: #生成一个长度为20地随即列表
In [14]: import random
In [15]: random.randint(1,10)Out[15]: 8In [16]: #它就会随即返回一个1-10之间随即地一个数
In [17]: random.randint(1,10)Out[17]: 10In [18]: #生成随即一个长度为20地列表：
In [19]: import random    ...:     ...: random_numbers = []    ...: while len(random_numbers) <= 20:    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers)    ...: [8, 10, 2, 3, 4, 5, 2, 3, 5, 1, 2, 9, 8, 3, 8, 1, 10, 2, 3, 4, 10]
In [20]: import random    ...:     ...: random_numbers = []    ...: while len(random_numbers) <= 20:    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers, len(random_numbers))    ...: [5, 9, 8, 8, 5, 5, 5, 1, 10, 3, 3, 1, 1, 6, 3, 5, 6, 9, 2, 2, 8] 21
In [21]: import random    ...:     ...: random_numbers = []    ...: while len(random_numbers) < 20:    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers, len(random_numbers))    ...: [10, 2, 8, 7, 1, 8, 4, 1, 4, 3, 8, 10, 5, 9, 4, 8, 10, 6, 7, 4] 20
In [22]: #如果那里是<=20，就会有个21，所以我们改成了<20 ↑
In [23]: #————————————————————————————————————————————————————————————————
In [24]: #编程建议：只要能使用for循环，就不要使用while循环。
In [25]: #一定要写import random
In [26]: import random
In [27]: #它跟模块是一样的，只要上面已经有导入过这个模块，下面就不用再写。
In [28]: random_numbers = []
In [29]: for i in range(20)
In [30]: File "<ipython-input-29-165a5f730222>", line 1 for i in range(20) ^SyntaxError: invalid syntax
list(range(20)) File "<ipython-input-30-32922625a043>", line 1 File "<ipython-input-29-165a5f730222>", line 1 ^SyntaxError: invalid syntax

In [31]: #这样就不行，如果打印一行：
In [32]: random_numbers = []
In [33]: for i in range(20):    ...: print(i)    ...: 012345678910111213141516171819
In [34]: #对于之前的例子也是一样的：
In [35]: random_numbers = []    ...: for i in range(20)    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers, len(random_numbers)) File "<ipython-input-35-65362b7b9dad>", line 2 for i in range(20) ^SyntaxError: invalid syntax

In [35]:
In [36]: random_numbers = []    ...: for i in range(20)：    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers, len(random_numbers)) File "<ipython-input-36-2a5ae58edc18>", line 2 for i in range(20)： ^SyntaxError: invalid character in identifier

In [37]: random_numbers = []    ...: for i in range(20):    ...: random_numbers.append(random.randint(1,10))    ...: print(random_numbers, len(random_numbers))    ...: [1, 1, 6, 3, 2, 10, 4, 10, 5, 1, 7, 5, 4, 6, 7, 9, 2, 8, 2, 10] 20
In [38]: #之前两个打错了啊，不要在意
In [39]: #为什么我要建议能用for，就不要while？
In [40]: #：因为写很多代码的时候，很容易将while循环写成死循环。
In [41]: #但是有些同学会说，我小心一点，不就行了吗？
In [42]: #：“小心一点”就意味着多花时间和精力。
In [43]: #————————————————————————————————————————————————————————————————
In [44]: #什么时候必须用while循环？
In [45]: #：当循环的条件跟数量没有关系时，只能用while循环。
In [46]: #————————————————————————————————————————————————————————————————
In [47]: #举个例子：往空列表中添加随即数，知道添加的数为9，则终止。
In [48]: #直到添加的数为9
In [49]: random_numbers = []
In [50]: while 9 not in random_numbers File "<ipython-input-50-d6db7c96a19f>", line 1 while 9 not in random_numbers ^SyntaxError: invalid syntax

In [51]: random_numbers = []    ...: while 9 not in random_numbers:    ...: random_numbers.append(random.randint(1,10))    ...:
In [52]: print(random_numbers, len(random_numbers))    ...:     ...:     ...:     ...: [6, 5, 4, 8, 10, 10, 9] 7
In [53]: #它就是说，本次随即生成第7次才会出现数字9。
In [54]: #————————————————————————————————————————————————————————————————
In [55]: #这次课程我们来点好玩的：留一个课后问题，大家自己去想想：
In [56]: print('\n问题：a = [1,2,3], b = 1, c = (b in a)，大家猜测一下，c是一个什么类型，它是不是一个元组呢？\n')
问题：a = [1,2,3], b = 1, c = (b in a)，大家猜测一下，c是一个什么类型，它是不是一个元组呢？

In [57]: print("\n本次“只读课堂”的python教程就到这了，欢迎继续收看！\n")
本次“只读课堂”的python教程就到这了，欢迎继续收看！

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