How to remove special characers from a column of dataframe using module re?

As this answer shows, you can use map() with a lambda function that will assemble and return any expression you like:

df['E'] = df['B'].map(lambda x: re.sub(r'\W+', '', x))

lambda simply defines anonymous functions. You can leave them anonymous, or assign them to a reference like any other object. my_function = lambda x: x.my_method(3) is equivalent to def my_function(x): return x.my_method(3).

A one liner without map is:

df['E'] = df['B'].str.replace('\W', '')