Python pandas doesn't recognize special charac

Question

I am trying to use df['column_name'].str.count("+") in python pandas, but I receive

"error: nothing to repeat"

. With the regular characters the method works, e.g. df['column_name'].str.count("a") works fine.

Also, there is a problem with the "^"-sign. If I use df['column_name'].str.contains("^") the result is incorrect - it looks like "^" gets interpreted as " " (empty space).

Surprisingly, if I use .count("+") and .contains("^") on a regular, non-pandas string they work perfectly fine.

simple working example:

df = pd.DataFrame({'column1': ['Nighthawks+', 'Dragoons'], 'column2': ['1st', '2nd']}, columns = ['column1', 'column2'])

When applying df["column1"].str.contains("^") one gets "True, True" but is should be "False, False".

And when applying df["column1"].str.count("+") one gets

"error: nothing to repeat"

But then, outside of panda, "bla++".count("+") gives correctly the result "2".

Any solutions? Thanks

Answer 1

You need to escape the plus sign:

In[10]:
df = pd.DataFrame({'a':['dsa^', '^++', '+++','asdasads']})
df

Out[10]: 
          a
0      dsa^
1       ^++
2       +++
3  asdasads

In[11]:
df['a'].str.count("\+")

Out[11]: 
0    0
1    2
2    3
3    0
Name: a, dtype: int64

Also when you do df['a'].str.count('^') this just returns 1 for all rows:

In[12]:
df['a'].str.count('^')

Out[12]: 
0    1
1    1
2    1
3    1
Name: a, dtype: int64

Again you need to escape the pattern:

In[16]:
df['a'].str.count('\^')

Out[16]: 
0    1
1    1
2    0
3    0
Name: a, dtype: int64

EDIT

Regarding the semantic difference between count on a normal string and on a Series, count on a python str just does a character count, but str.count takes a regex pattern. The ^ and + are special characters which need to be escaped with a backslash if you are searching for those characters