| # |
| # Licensed to the Apache Software Foundation (ASF) under one or more |
| # contributor license agreements. See the NOTICE file distributed with |
| # this work for additional information regarding copyright ownership. |
| # The ASF licenses this file to You under the Apache License, Version 2.0 |
| # (the "License"); you may not use this file except in compliance with |
| # the License. You may obtain a copy of the License at |
| # |
| # http://www.apache.org/licenses/LICENSE-2.0 |
| # |
| # Unless required by applicable law or agreed to in writing, software |
| # distributed under the License is distributed on an "AS IS" BASIS, |
| # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| # See the License for the specific language governing permissions and |
| # limitations under the License. |
| # |
| |
| """ |
| Module defining global singleton classes. |
| |
| This module raises a RuntimeError if an attempt to reload it is made. In that |
| way the identities of the classes defined here are fixed and will remain so |
| even if pyspark itself is reloaded. In particular, a function like the following |
| will still work correctly after pyspark is reloaded: |
| |
| def foo(arg=pyspark._NoValue): |
| if arg is pyspark._NoValue: |
| ... |
| |
| See gh-7844 for a discussion of the reload problem that motivated this module. |
| |
| Note that this approach is taken after from NumPy. |
| """ |
| |
| __ALL__ = ['_NoValue'] |
| |
| |
| # Disallow reloading this module so as to preserve the identities of the |
| # classes defined here. |
| if '_is_loaded' in globals(): |
| raise RuntimeError('Reloading pyspark._globals is not allowed') |
| _is_loaded = True |
| |
| |
| class _NoValueType(object): |
| """Special keyword value. |
| |
| The instance of this class may be used as the default value assigned to a |
| deprecated keyword in order to check if it has been given a user defined |
| value. |
| |
| This class was copied from NumPy. |
| """ |
| __instance = None |
| |
| def __new__(cls): |
| # ensure that only one instance exists |
| if not cls.__instance: |
| cls.__instance = super(_NoValueType, cls).__new__(cls) |
| return cls.__instance |
| |
| # needed for python 2 to preserve identity through a pickle |
| def __reduce__(self): |
| return (self.__class__, ()) |
| |
| def __repr__(self): |
| return "<no value>" |
| |
| |
| _NoValue = _NoValueType() |