Python外壳:代码结构
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Python的独特语法:
- 不使用分号结束语句,而是回车;
- 通过代码缩进来区分代码块;
- if、while、for等,都不用括号,但不能没有冒号(:)。
如何将一行命令分为多行?
>>> myNameIs = "LiZhiXin." >>> myNameIs ‘LiZhiXin.‘
4.1 条件语句和循环语句
如何使用if、elif和else进行比较?
>>> a = 1 >>> if a < 2: print ("yes") elif a > 2: print ("no") else: print ("chaos") yes
如何连接条件表达式?
python中没有!、&& 和 || 运算符,分别用 not、and 和 or代替。
>>> not 1 False >>> 5 < 6 and 1 < 2 True >>> 5 < 6 or 1 > 2 True
python中有哪些假值?
>>> False False >>> None >>> 0 0 >>> 0.0 0.0 >>> ‘‘ ‘‘ >>> [] [] >>> () () >>> {} {} >>> set() set()
如何使用while进行循环?
>>> count = 1 >>> while count <= 5: print(count) count += 1 1 2 3 4 5
如何跳出循环?
>>> while True: stuff = input("string to calpitalize [type q to quit]:") if stuff == ‘q‘: break print(stuff.capitalize()) string to calpitalize [type q to quit]:li zhi xin Li zhi xin string to calpitalize [type q to quit]:q >>>
如何跳到循环开始(用于跳过特定条件的循环)?
>>> while True: value = input("Interger, please [q to quit]: ") if value == ‘q‘: break number = int(value) if number % 2 == 0: continue print(number, "squared is ", number*number) Interger, please [q to quit]: 1 1 squared is 1 Interger, please [q to quit]: 2 Interger, please [q to quit]: 3 3 squared is 9 Interger, please [q to quit]: 4 Interger, please [q to quit]: q
循环外的else是如何使用的?
>>> numbers = [1,3,5] >>> position = 0 >>> while position < len(numbers): number = numbers[position] if number % 2 == 0: print(‘Found even number‘, number) break position += 1 else: print("No even number found.") No even number found.
*如何使用for进行迭代(很独特)?
python中的for很牛逼,可以在数据结构和具体实现未知的情况下,遍历整个数据结构:
>>> rabbits = [‘a‘, ‘b‘, ‘c‘, ‘d‘] >>> current = 0 >>> while current < len(rabbits): print(rabbits[current]) current += 1 a b c d >>> for rabbit in rabbits: print(rabbit) a b c d
>>> word = ‘cat‘ >>> for letter in word: print(letter) c a t
>>> a = {‘a‘:‘b‘, ‘c‘:‘d‘, ‘e‘:‘f‘} >>> for key in a: print(key) a c e
>>> for value in a.values(): print(value) b d f
>>> for item in a.items(): print(item) (‘a‘, ‘b‘) (‘c‘, ‘d‘) (‘e‘, ‘f‘)
>>> for key, value in a.items(): print(key, value) a b c d e f
如何用zip()函数进行迭代?
对多个序列使用并行迭代,就是一起迭代,等价于将多个序列有序合并了。
>>> c = 0.1, 0.2, 0.3 >>> a = (1, 2, 3) >>> b = [‘a‘, ‘b‘, ‘c‘, ‘d‘] >>> c = 0.1, 0.2, 0.3, 0.4, 0.5, >>> for e, f, g in zip(a, b, c): print(e, ‘ ‘, f, ‘ ‘, g) 1 a 0.1 2 b 0.2 3 c 0.3
list()、zip()和 dict()可以灵活运用。
如何生成特定区间的自然数序列?
range()的使用方法类似切片,但是却是使用‘,’分隔,而不是‘:’。
>>> for x in range(0,3): print(x) 0 1 2 >>> list(range(0,3)) [0, 1, 2]
4.2 推导式(python特有)
从一个或多个迭代器创建数据结构,可以将循环和条件结合。
列表推导式
>>> number_list = [number for number in range(1,6)] >>> number_list [1, 2, 3, 4, 5]
>>> a_list = [number for number in range(1,6) if number % 2 ==1] >>> a_list [1, 3, 5]
>>> rows = range(1,4) >>> cols = range(1,3) >>> cells = [(row, col) for row in rows for col in cols] >>> for cell in cells: print(cell) (1, 1) (1, 2) (2, 1) (2, 2) (3, 1) (3, 2)
字典推导式
>>> word = ‘letters‘ >>> letter_counts = {letter:word.count(letter) for letter in word} >>> letter_counts {‘l‘: 1, ‘t‘: 2, ‘r‘: 1, ‘s‘: 1, ‘e‘: 2}
函数
python中参数有哪几种使用方法?
>>> def func(a, b, c): print(‘a is ‘, a, ‘b is ‘, b, ‘c is ‘, c) >>> func(1, 2, 3) a is 1 b is 2 c is 3
>>> func(c = 1, b = 2, a = 3) a is 3 b is 2 c is 1
>>> d = [1, 2, 3] >>> func(*d) a is 1 b is 2 c is 3
>>> e = {‘c‘:1, ‘b‘:2, ‘a‘:3} >>> func(**e) a is 3 b is 2 c is 1
生成器
装饰器
命名空间和作用域
异常
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