## What changes were proposed in this pull request?
This PR proposes to remove incorrect implementation that has been not executed so far (at least from Spark 1.5.2) for `in` operator and throw a correct exception rather than saying it is a bool. I tested the codes above in 1.5.2, 1.6.3, 2.1.0 and in the master branch as below:
**1.5.2**
```python
>>> df = sqlContext.createDataFrame([[1]])
>>> 1 in df._1
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark-1.5.2-bin-hadoop2.6/python/pyspark/sql/column.py", line 418, in __nonzero__
raise ValueError("Cannot convert column into bool: please use '&' for 'and', '|' for 'or', "
ValueError: Cannot convert column into bool: please use '&' for 'and', '|' for 'or', '~' for 'not' when building DataFrame boolean expressions.
```
**1.6.3**
```python
>>> 1 in sqlContext.range(1).id
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark-1.6.3-bin-hadoop2.6/python/pyspark/sql/column.py", line 447, in __nonzero__
raise ValueError("Cannot convert column into bool: please use '&' for 'and', '|' for 'or', "
ValueError: Cannot convert column into bool: please use '&' for 'and', '|' for 'or', '~' for 'not' when building DataFrame boolean expressions.
```
**2.1.0**
```python
>>> 1 in spark.range(1).id
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark-2.1.0-bin-hadoop2.7/python/pyspark/sql/column.py", line 426, in __nonzero__
raise ValueError("Cannot convert column into bool: please use '&' for 'and', '|' for 'or', "
ValueError: Cannot convert column into bool: please use '&' for 'and', '|' for 'or', '~' for 'not' when building DataFrame boolean expressions.
```
**Current Master**
```python
>>> 1 in spark.range(1).id
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark/python/pyspark/sql/column.py", line 452, in __nonzero__
raise ValueError("Cannot convert column into bool: please use '&' for 'and', '|' for 'or', "
ValueError: Cannot convert column into bool: please use '&' for 'and', '|' for 'or', '~' for 'not' when building DataFrame boolean expressions.
```
**After**
```python
>>> 1 in spark.range(1).id
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark/python/pyspark/sql/column.py", line 184, in __contains__
raise ValueError("Cannot apply 'in' operator against a column: please use 'contains' "
ValueError: Cannot apply 'in' operator against a column: please use 'contains' in a string column or 'array_contains' function for an array column.
```
In more details,
It seems the implementation intended to support this
```python
1 in df.column
```
However, currently, it throws an exception as below:
```python
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File ".../spark/python/pyspark/sql/column.py", line 426, in __nonzero__
raise ValueError("Cannot convert column into bool: please use '&' for 'and', '|' for 'or', "
ValueError: Cannot convert column into bool: please use '&' for 'and', '|' for 'or', '~' for 'not' when building DataFrame boolean expressions.
```
What happens here is as below:
```python
class Column(object):
def __contains__(self, item):
print "I am contains"
return Column()
def __nonzero__(self):
raise Exception("I am nonzero.")
>>> 1 in Column()
I am contains
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 6, in __nonzero__
Exception: I am nonzero.
```
It seems it calls `__contains__` first and then `__nonzero__` or `__bool__` is being called against `Column()` to make this a bool (or int to be specific).
It seems `__nonzero__` (for Python 2), `__bool__` (for Python 3) and `__contains__` forcing the the return into a bool unlike other operators. There are few references about this as below:
https://bugs.python.org/issue16011http://stackoverflow.com/questions/12244074/python-source-code-for-built-in-in-operator/12244378#12244378http://stackoverflow.com/questions/38542543/functionality-of-python-in-vs-contains/38542777
It seems we can't overwrite `__nonzero__` or `__bool__` as a workaround to make this working because these force the return type as a bool as below:
```python
class Column(object):
def __contains__(self, item):
print "I am contains"
return Column()
def __nonzero__(self):
return "a"
>>> 1 in Column()
I am contains
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: __nonzero__ should return bool or int, returned str
```
## How was this patch tested?
Added unit tests in `tests.py`.
Author: hyukjinkwon <gurwls223@gmail.com>
Closes#17160 from HyukjinKwon/SPARK-19701.
224e0e785b