2021-09-25

主要内容：Python基础知识/基础语法；算法：事件/空间复杂度

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python idiom

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python *args , **kwargs

类似这样的：

解释："The single asterisk form (*args) is used to pass a non-keyworded, variable-length argument list, and the double asterisk form is used to pass a keyworded, variable-length argument list." (来自https://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/)

一些简单的例子帮助快速入门，见https://stackoverflow.com/questions/36901/what-does-double-star-asterisk-and-star-asterisk-do-for-parameters

（针对上面的stackoverflow链接）一些补充代码：

def bar(**kwargs):
    for a in kwargs:
        print(a, kwargs[a])

bar(name='one', age=27)

# name one
# age 27

========================================================


def bar(**kwargs):
    for a in kwargs:
        print(a, kwargs[a])


dict = {'name': 'one', 'age': 27}
bar(dict)

# TypeError: bar() takes 0 positional arguments but 1 was given

========================================================

def bar(**kwargs):
    for a in kwargs:
        print(a, kwargs[a])


dict = {'name': 'one', 'age': 27}
bar(name='one', age=27, dict=dict)

# name one
# age 27
# dict {'name': 'one', 'age': 27}

========================================================

def bar(*x, **y):
    for item in x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


bar(1, 2, 3, 4, name='student', age='24')

# 1
# 2
# 3
# 4
# name:student
# age:24

======================================================

def bar(*x, **y):
    for item in x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


bar((1, 2, 3, 4), name='student', age='24')

# (1, 2, 3, 4)
# name:student
# age:24

======================================================

def bar(*x, **y):
    for item in x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


bar(1, 2, 3, 4, name='student', age='24', 5, 6)

#     bar(1, 2, 3, 4, name='student', age='24', 5, 6)
#                                              ^
# SyntaxError: positional argument follows keyword argument

此外，这个链接：https://www.saltycrane.com/blog/2008/01/how-to-use-args-and-kwargs-in-python/ 也列举了一些*args和**kwargs的代码。

如果运行下面的3个代码片段：

def bar(*x, **y):
    for item in x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


l = [1, 2, 3, 4]
bar(l, name='student', age='24')

# [1, 2, 3, 4]
# name:student
# age:24





def bar(*x, **y):
    def printx(x_x):
        for i in x_x: print(i)

    printx(*x)
    for item in y:
        print(item + ':' + y[item])


l = [1, 2, 3, 4]
bar(l, name='student', age='24')


# 1
# 2
# 3
# 4
# name:student
# age:24



def bar(*x, **y):
    for item in *x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


l = [1, 2, 3, 4]
bar(l, name='student', age='24')


#     for item in *x:
#                 ^
# SyntaxError: invalid syntax

第3个代码片段会报错，那么如何把它改正确呢？

应该这么修改（修改了line 9）：

def bar(*x, **y):
    for item in x:
        print(item)
    for item in y:
        print(item + ':' + y[item])


l = [1, 2, 3, 4]
bar(*l, name='student', age='24')


# 1
# 2
# 3
# 4
# name:student
# age:24

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python lambda : map function

list1 = [1, 2, 3, 4, 5]
list1_r = list(map(lambda item: item, list1))
print(list1_r)
# 2.283333333333333



list1 = [1, 2, 3, 4, 5]
list1_r = sum(map(lambda item: item, list1))
print(list1_r)
# 15



list1 = [1, 2, 3, 4, 5]
list1_r = list(map(lambda item: 1 / item, list1))
print(list1_r)
# [1.0, 0.5, 0.3333333333333333, 0.25, 0.2]

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python判断string是否为数字：（比如'1234': yes和'1234k': no）

https://stackoverflow.com/questions/354038/how-do-i-check-if-a-string-is-a-number-float

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python console I/O

代码举例：

nargs参数的含义与作用：https://stackoverflow.com/questions/20165843/argparse-how-to-handle-variable-number-of-arguments-nargs

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python overload

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给定一组统计数据（比如运行时间），如何衡量这组数据“很稳定”（浮动不大）？

使用Coefficient of variation（CV），见：https://en.wikipedia.org/wiki/Coefficient_of_variation

[mathjax-d]\displaylines{ CV=\frac{\sigma}{\mu} \\ \sigma: \text{standard deviation} \\ \mu: \text{mean} }[/mathjax-d]

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