带条件的Python控件“with”上下文管理器

Question

Python2.7是否可以使用条件来控制“with”上下文管理器？我的场景是，如果gzip文件存在，我想附加到它，如果它不存在，我想写入一个新文件。伪代码是：

with gzip.open(outfile, 'a+') if os.isfile(outfile) else with open(outfile, 'w') as outhandle:

或者

if os.isfile(outfile):
    with gzip.open(outfile, 'a+') as outhandle:
        # do stuff
else:
    with open(outfile, 'w') as outhandle:
        # do the same stuff

我不想重复“做事情”，因为他们之间是一样的。但是如何使用条件来控制上下文呢

Answer 1

你可以试着为“do stuff”写一个函数

def do_stuff():
    #do stuff here 

if os.isfile(outfile):
    with gzip.open(outfile, 'a+') as outhandle:
        do_stuff()
else:
    with open(outfile, 'w') as outhandle:
        do_stuff()

Answer 2

记住，函数也可以分配给变量

if os.isfile(outfile):
    open_function = gzip.open
    mode = 'a+'
else:
    open_function = open
    mode = 'w'

with open_function(outfile, mode) as outhandle:
    # do stuff