String manipulation

Regular expressions

# Extract strings with a specific regex
df= df['col_name'].str.extract[r'[Aa-Zz]']

# Replace strings within a regex
df['col_name'].str.replace('Replace this', 'With this')

For information on how to match strings using regex, see Getting started with Regular Expressions.

Slicing strings

Strings in a Series can be sliced using .str.slice() method, or more conveniently, using brackets (.str[]).

In [1]: ser = pd.Series(['Lorem ipsum', 'dolor sit amet', 'consectetur adipiscing elit'])
In [2]: ser
Out[2]: 
0                    Lorem ipsum
1                 dolor sit amet
2    consectetur adipiscing elit
dtype: object

Get the first character of each string:

In [3]: ser.str[0]
Out[3]: 
0    L
1    d
2    c
dtype: object

Get the first three characters of each string:

In [4]: ser.str[:3]
Out[4]: 
0    Lor
1    dol
2    con
dtype: object

Get the last character of each string:

In [5]: ser.str[-1]
Out[5]:
0    m
1    t
2    t
dtype: object

Get the last three characters of each string:

In [6]: ser.str[-3:]
Out[6]: 
0    sum
1    met
2    lit
dtype: object

Get the every other character of the first 10 characters:

In [7]: ser.str[:10:2]
Out[7]: 
0    Lrmis
1    dlrst
2    cnett
dtype: object

Pandas behaves similarly to Python when handling slices and indices. For example, if an index is outside the range, Python raises an error:

In [8]:'Lorem ipsum'[12]
# IndexError: string index out of range

However, if a slice is outside the range, an empty string is returned:

In [9]: 'Lorem ipsum'[12:15]
Out[9]: ''

Pandas returns NaN when an index is out of range:

In [10]: ser.str[12]
Out[10]:
0    NaN
1      e
2      a
dtype: object

And returns an empty string if a slice is out of range:

In [11]: ser.str[12:15]
Out[11]:
0       
1     et
2    adi
dtype: object

Checking for contents of a string

str.contains() method can be used to check if a pattern occurs in each string of a Series. str.startswith() and str.endswith() methods can also be used as more specialized versions.

In [1]: animals = pd.Series(['cat', 'dog', 'bear', 'cow', 'bird', 'owl', 'rabbit', 'snake'])

Check if strings contain the letter ‘a’:

In [2]: animals.str.contains('a')
Out[2]:
0      True
1     False
2      True
3     False
4     False
5     False
6      True
7      True
8      True
dtype: bool

This can be used as a boolean index to return only the animals containing the letter ‘a’:

In [3]: animals[animals.str.contains('a')]
Out[3]: 
0       cat
2      bear
6    rabbit
7     snake
dtype: object

str.startswith and str.endswith methods work similarly, but they also accept tuples as inputs.

In [4]: animals[animals.str.startswith(('b', 'c'))]
# Returns animals starting with 'b' or 'c'
Out[4]: 
0     cat
2    bear
3     cow
4    bird
dtype: object

Capitalization of strings

In [1]: ser = pd.Series(['lORem ipSuM', 'Dolor sit amet', 'Consectetur Adipiscing Elit'])

Convert all to uppercase:

In [2]: ser.str.upper()
Out[2]:
0                    LOREM IPSUM
1                 DOLOR SIT AMET
2    CONSECTETUR ADIPISCING ELIT
dtype: object

All lowercase:

In [3]: ser.str.lower()
Out[3]:
0                    lorem ipsum
1                 dolor sit amet
2    consectetur adipiscing elit
dtype: object

Capitalize the first character and lowercase the remaining:

In [4]: ser.str.capitalize()
Out[4]:
0                    Lorem ipsum
1                 Dolor sit amet
2    Consectetur adipiscing elit
dtype: object

Convert each string to a titlecase (capitalize the first character of each word in each string, lowercase the remaining):

In [5]: ser.str.title()
Out[5]:
0                    Lorem Ipsum
1                 Dolor Sit Amet
2    Consectetur Adipiscing Elit
dtype: object

Swap cases (convert lowercase to uppercase and vice versa):

In [6]: ser.str.swapcase()
Out[6]:
0                    LorEM IPsUm
1                 dOLOR SIT AMET
2    cONSECTETUR aDIPISCING eLIT
dtype: object

Aside from these methods that change the capitalization, several methods can be used to check the capitalization of strings.

In [7]: ser = pd.Series(['LOREM IPSUM', 'dolor sit amet', 'Consectetur Adipiscing Elit'])

Check if it is all lowercase:

In [8]: ser.str.islower()
Out[8]:
0    False
1     True
2    False
dtype: bool

Is it all uppercase:

In [9]: ser.str.isupper()
Out[9]:
0     True
1    False
2    False
dtype: bool

Is it a titlecased string:

In [10]: ser.str.istitle()
Out[10]:
0    False
1    False
2     True
dtype: bool