Python3编程：实用代码片段集合

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"这篇文档是关于Python3编程中常用代码块的集合，涵盖了字符串操作、循环控制、进制转换和自定义异常等多个方面。" 在Python3中，字符串是编程中非常基础且重要的数据类型。字符串可以用单引号或双引号包围，如果需要在字符串中包含双引号，可以使用反斜杠(\)进行转义，如`'I l\"o\"ve fishc.com'`。字符串支持切片操作，例如`Str1[:6]`会返回字符串`Str1`的前六个字符。字符串方法如`.capitalize()`会返回一个新的首字母大写的新字符串，原始字符串不会改变。字符串的连接可以通过`+`操作符实现，如`print("nihao"+"a")`会输出`nihaoa`。字符串乘以整数会重复输出该字符串，例如`print("nihao\n"*3)`将输出`nihao`三遍，每行一个。`print`函数的`end`参数可以用来改变默认的换行符，例如`print("不分手的",end="恋爱")`会在不换行的情况下输出`恋爱`。获取字符串长度可以使用内置的`len()`函数，例如`len("chilema")`返回7。而`str1.join("12345")`则会将"12345"中的每个字符用"sh"连接起来，结果为`'1sh2sh3sh4sh5'`。在进制转换方面，`bin(10)`会将十进制数10转换为二进制表示，结果为`'0b1010'`。在循环控制中，Python的`for...else...`结构可以用于在循环结束后执行特定代码，除非`break`语句被触发。例如，多重循环中，当满足条件时跳出所有循环。同时，通过设置`flag`变量可以更灵活地控制循环的中断。此外，还可以自定义异常，例如创建一个名为`StopLoopError`的异常类，可以在循环中捕获并抛出，以达到提前结束循环的目的。这些代码块展示了Python3编程中常见的实用技巧，对于日常开发和学习都十分有帮助。通过理解和掌握这些知识，可以提高编程效率，使代码更加简洁易懂。

need to reduce it.

from functools import partial

f = partial(dist, origin)

print(sorted(l, key=f))

# you can also use lambda function

print(sorted(l, key=lambda x: dist(x, origin)))

四、容器及其操作四、容器及其操作

集合集合Set

#modify sets

>>> example1 = set()

>>> example1.add("yi")

>>> example1.add("er")

>>> example2 = set([28, True, 3.14, "nihao", "yi", "er"])

>>> len(example)

>>> example2.clear()

#evaluate union and intersection of two sets

>>> example1.union(example2)

>>> example1.intersection(example2)

>>> "nihao" in example2

True

>>> "nihao" not in example2

False

元组元组Tuple

一旦定义，不能改变，不能再赋值，不能用del删除某个元素，只能删除整个元组

元组的切片方法和列表一样

创建空元组：temp=()

创建一个数的元组：temp=(1,) 必须加逗号，括号可以不加

改变一个元组的办法，例如 temp=(1,2,3,4)，令 temp = temp[:2] + (6,) + temp[2:] 输出temp 为 (1,2,6,3,4)，这是元组的拼接，同样适用于字符串。

>>> temp = 1,2,3

>>>temp

(1, 2, 3)

>>> 8*(8,)

(8, 8, 8, 8, 8, 8, 8, 8)

Unzip a list of tuples

zipped_list = [(1, 'a'), (2, 'b'), (3, 'c')] list_a, list_b = zip(*zipped_list)

print(list_a)

# out: (1,2,3)

print(list_b)

# out: ('a', 'b', 'c')

Iterators returns only elements at a time. len function cannot be used with iterators. We can loop over the zip object or the iterator to get the actual list.

list_a = [1, 2, 3] list_b = [4, 5, 6]

zipped = zip(a, b) # out: zip object

len(zipped) = # out: TypeError: object of type 'zip' has no len()

zipped[0] # out: zip object is not subscriptable

list_c = list(zipped) # out: [(1,4), (2,5), (3,6)] list_d = list(zipped) # out: [] is empty list because of the above statement

Named tuples

Named tuples subclass tuple, and add a layer to assign property names to the potential elements. It is located in the collections standard library module.

Named tuples are also regular tuples, we can still handle them just like any other tuple(by index, slice, iterate). Named tuples are immutable.

from collections import namedtuple

'''it is a function(class factory) which generates(return) a new class that

inherits from tuple. The new class provides named properties to access

elements of the tuple and an instance of that class is still a tuple'''

'''namedtuple needs a few things to generate this class:

1.the class name we want to use

2.a sequence(list, tuple) of field names(strings) we want to assign, in the order of the elements in that tuple

'''

Point2D = namedtuple('Point2D', ['x', 'y']) # the variable initial is capitalized, because it receives a class returned from the fucntion

#the following three ones have the same effect

#Point2D = namedtuple('Point2D', ('x', 'y'))

#Point2D = namedtuple('Point2D', 'x, y')

#Point2D = namedtuple('Point2D', 'x y')

'''in fact, the __new__ method of the generated class uses the field names we provided as param names'''

# we can easily find out the field names in a named tuple generated class

>>> Point2D._fields

('x', 'y')

>>> print(Point2D._source)

... # print out what the class is

>>> pt = Point2D(10, 20)

>>> isinstance(pt, tuple)

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