[英]Is there a cleaner way to chain empty list checks in Python?
我有一个相当复杂的对象(反序列化的json,所以我没有太多的控制权)我需要检查是否存在并迭代一个相当深的元素,所以现在我有这样的东西:
if a.get("key") and a["key"][0] and a["key"][0][0] :
for b in a["key"][0][0] :
#Do something
哪个有效,但很难看。 似乎必须有更好的方法来做到这一点,那么什么是更优雅的解决方案?
try:
bs = a["key"][0][0]
# Note: the syntax for catching exceptions is different in old versions
# of Python. Use whichever one of these lines is appropriate to your version.
except KeyError, IndexError, TypeError: # Python 3
except (KeyError, IndexError, TypeError): # Python 2
bs = []
for b in bs:
如果你不介意更长的行,你可以把它打包成一个函数:
def maybe_list(f):
try:
return f()
except KeyError, IndexError, TypeError:
return []
for b in maybe_list(lambda: a["key"][0][0]):
我会编写一个自定义索引器函数,如下所示:
def safe_indexer(obj, *indices):
for idx in indices:
if not obj: break
if hasattr(obj, "get"):
obj = obj.get(idx)
else:
obj = obj[idx]
return obj
用法:
a = {"key": {0: {0: "foo"} } };
print safe_indexer(a, "key", 0, 0)
print safe_indexer(a, "bad", 0, 0)
输出:
foo
None
那这个呢:
try:
for b in a['key'][0][0]:
# do stuff.
except KeyError, TypeError, IndexError:
# respond appropriately.
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