python how to check if a string is an element of a list of strings [duplicate]

You can use the vectorised str.contains to test if a string is present/contained in each row :

In [262]:
testData['value'].str.contains(testData['value'][0])

Out[262]:
0     True
1    False
2    False
Name: value, dtype: bool

If you're after whether it's present in any row then use any:

In [264]:
testData['value'].str.contains(testData['value'][0]).any()

Out[264]:
True

OK to address your last question:

In [270]:
testData['value'][0] in testData['value']

Out[270]:
False

This is because pd.Series.__contains__ is implemented:

def __contains__(self, key):
    """True if the key is in the info axis"""
    return key in self._info_axis

If we look at what _info_axis actually is:

In [269]:
testData['value']._info_axis

Out[269]:
RangeIndex(start=0, stop=3, step=1)

Then we can see when we do 'abc' in testData['value'] we're really testing whether 'abc' is actually in the index which is why it returns False

Example:

In [271]:
testData=pd.DataFrame({'value':['abc','cde','fgh']}, index=[0, 'turkey',2])
testData

Out[271]:
       value
0        abc
turkey   cde
2        fgh

In [272]:
'turkey' in testData['value']

Out[272]:
True

We can see that is returns True now because we're testing if 'turkey' is present in the index