无穷嵌套的列表
>>> a = [1, 2, 3, 4] >>> a.append(a) >>> a [1, 2, 3, 4, [...]] >>> a[4] [1, 2, 3, 4, [...]] >>> a[4][4][4][4][4][4][4][4][4][4] == a True
无穷嵌套的字典
>>> a = {} >>> b = {} >>> a['b'] = b >>> b['a'] = a >>> print a {'b': {'a': {...}}}
列表重构
>>> l = [[1, 2, 3], [4, 5], [6], [7, 8, 9]] >>> sum(l, []) [1, 2, 3, 4, 5, 6, 7, 8, 9]
或者
import itertools data = [[1, 2, 3], [4, 5, 6]] list(itertools.chain.from_iterable(data))
再或者
from functools import reduce from operator import add data = [[1, 2, 3], [4, 5, 6]] reduce(add, data)
字典生成
>>> {a:a**2 for a in range(1, 10)} {1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}
类中方法重置
class foo:
def normal_call(self):
print("normal_call")
def call(self):
print("first_call")
self.call = self.normal_call
>>> y = foo()
>>> y.call() first_call >>> y.call() normal_call >>> y.call() normal_call
获取类属性
class GetAttr(object):
def __getattribute__(self, name):
f = lambda: "Hello {}".format(name) return f>>> g = GetAttr() >>> g.Mark()
'Hello Mark'
集合
>>> a = set([1,2,3,4]) >>> b = set([3,4,5,6]) >>> a | b # Combining{1, 2, 3, 4, 5, 6} >>> a & b # Intersection{3, 4} >>> a < b # SubsetsFalse>>> a - b # Variance{1, 2} >>> a ^ b # The symmetric difference{1, 2, 5, 6}
集合定义必须使用set关键字, 除非使用集合生成器
{ x for x in range(10)} # Generator sets
set([1, 2, 3]) == {1, 2, 3} set((i*2 for i in range(10))) == {i*2 for i in range(10)}
比较操作
>>> x = 5
>>> 1 < x < 10
True
>>> 10 < x < 20
False
>>> x < 10 < x*10 < 100
True
>>> 10 > x <= 9
True
>>> 5 == x > 4
True
动态创建新类
>>> NewType = type("NewType", (object,), {"x": "hello"}) >>> n = NewType() >>> n.x'hello'
另一个普通版本
>>> class NewType(object): >>> x = "hello" >>> n = NewType() >>> n.x"hello"
条件赋值
x = 1 if (y == 10) else 2
x = 3 if (y == 1) else 2 if (y == -1) else 1
变量解包
>>> first,second,*rest = (1,2,3,4,5,6,7,8) >>> first # The first value1
>>> second # The second value2
>>> rest # All other values
[3, 4, 5, 6, 7, 8]>>> first,*rest,last = (1,2,3,4,5,6,7,8) >>> first1>>> rest [2, 3, 4, 5, 6, 7] >>> last8
列表元素的序号
>>> l = ["spam", "ham", "eggs"] >>> list(enumerate(l)) >>> [(0, "spam"), (1, "ham"), (2, "eggs")] >>> list(enumerate(l, 1)) # 指定计数起点
>>> [(1, "spam"), (2, "ham"), (3, "eggs")]
异常捕获中使用else
try: function()
except Error: # If not load the try and declared Error
else: # If load the try and did not load except
finally: # Performed anyway
列表拷贝
错误的做法
>>> x = [1, 2, 3] >>> y = x >>> y[2] = 5>>> y [1, 2, 5] >>> x [1, 2, 5]
正确的做法
>>> x = [1,2,3] >>> y = x[:] >>> y.pop()3>>> y [1, 2] >>> x [1, 2, 3]
对于递归列表的做法
import copy my_dict = {'a': [1, 2, 3], 'b': [4, 5, 6]} my_copy_dict = copy.deepcopy(my_dict)
英文原文: https://www.devbattles.com/en/sand/post-1799-Python_the_things_that_you_might_not_know
译者: 诗书塞外