Python借助with语句实现代码段只执行有限次

a = 0
for i in range(3):
    a += 1
print(a)

a = 0
for i in range(3):
    print(type(a))
    a += 1
print(a)
''' 打印结果：
<class 'int'>
<class 'int'>
<class 'int'>
3
'''

from typing import Any


class LimitedRun(object):
    run_dict = {}

    def __init__(self,
                 tag: Any = 'default',
                 limit: int = 1):
        self.tag = tag
        self.limit = limit

    def __enter__(self):
        if self.tag in LimitedRun.run_dict.keys():
            LimitedRun.run_dict[self.tag] += 1
        else:
            LimitedRun.run_dict[self.tag] = 1
        return LimitedRun.run_dict[self.tag] <= self.limit

    def __exit__(self, exc_type, exc_value, traceback):
        return

tag是标签，相同标签共用执行次数计数器；limit是限制执行的次数。例子如下：

a = 0
for i in range(3):
    with LimitedRun('print_1', 1) as limited_run:
        if limited_run:
            print(type(a))
    a += 1
print(a)

a = 0
for i in range(3):
    with LimitedRun('print_1', 4) as limited_run:
        if limited_run:
            print(1, type(a))
    a += 1
for i in range(3):
    with LimitedRun('print_1', 4) as limited_run:
        if limited_run:
            print(2, type(a))
    a += 1
print(a)

a = 0
for i in range(3):
    with LimitedRun('print_1', 4) as limited_run:
        if limited_run:
            print(1, type(a))
    a += 1
for i in range(3):
    with LimitedRun('print_2', 4) as limited_run:
        if limited_run:
            print(2, type(a))
    a += 1
print(a)