caijialiang created AMBARI-25997:
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Summary: Improvement and Bug Fix in ambari_server.properties.py
Key: AMBARI-25997
URL: https://issues.apache.org/jira/browse/AMBARI-25997
Project: Ambari
Issue Type: Bug
Affects Versions: 2.7.7, 2.8.0
Reporter: caijialiang
File Location: ambari-server/src/main/python/ambari_server/properties.py
Problem Description:
1. The `__getattr__` method is used for dynamic proxying of methods. In the
case where `hasattr(self._props, name)` is false indicating the corresponding
method or attribute cannot be found, an exception needs to be thrown. If not,
it may confuse the user and obstruct code debugging.
2. The class `Properties` proxies the `has_key` method to the `dict` object
through `__getattr__`, which is acceptable: `Properties().has_key("x")`.
However, for the operation `"x" in Properties()`, it ends up in an infinite
hang, never returning. Therefore, a `__contains__` method needs to be
implemented to keep consistency with the logic of `has_key`, i.e., to determine
whether the object is in `_props`:
```python
def __contains__(self, key):
return key in self._props
```
This modification prevents the infinite hang problem from occurring.
To reproduce the hang issue, we can make a simplified version of the
`Properties` class for testing, as follows:
```python
#!/usr/bin/env python
import os
import re
import time
class Properties(object):
def __init__(self, props=None):
self._props = {}
self._origprops = {}
self._keymap = {}
def get_property(self, key):
return self._props.get(key, '')
def propertyNames(self):
return self._props.keys()
def getPropertyDict(self):
return self._props
def __getitem__(self, name):
return self.get_property(name)
def __getattr__(self, name):
try:
return self.__dict__[name]
except KeyError:
if hasattr(self._props, name):
return getattr(self._props, name)
else:
raise NotImplementedError("The method '{}' is not
implemented.".format(name))
def __contains__(self, key):
return key in self._props
if __name__ == "__main__":
p = Properties()
"a" in p
```
Upon running this program with either Python 3 or Python 2 python, it will
indefinitely hang, never returning.
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