python - 检查变量是否存在

Question

我正在使用以下方法 isset(var) 来确定变量是否存在。

def isset(variable):
    try:
        variable
    except NameError:
        return False
    else:
        return True

如果变量存在，它返回 True。但如果变量不存在，我会得到以下信息:

Traceback (most recent call last):
  File "/usr/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/home/lenovo/pyth/master/vzero/__main__.py", line 26, in <module>
    ss.run()
  File "vzero/ss.py", line 4, in run
    snap()
  File "vzero/ss.py", line 7, in snap
    core.display()
  File "vzero/core.py", line 77, in display
    stdout(session(username()))
  File "vzero/core.py", line 95, in session
    if isset(ghi): #current_sessions[user]):
NameError: global name 'ghi' is not defined

我不想要所有这些错误。我只希望它返回 False。无输出。我该怎么做？

Answer 1

而不是编写一个复杂的辅助函数 isset 并调用它

if not isset('variable_name'):
    # handle the situation

在你想检查变量是否存在的地方做:

try:
    # some code with the variable in question
except NameError:
    # handle the situation