What are common ways to manipulate strings?

Practicing Coding Interview Questions in Python

Kirill Smirnov

Data Science Consultant, Altran

String

Create strings:

s = 'hello'
print(s)

hello

s = "hello"
print(s)

hello

String

str() constructor:

str("hello")

'hello'

str(11.5)

'11.5'

str([1, 2, 3])

'[1, 2, 3]'

str() constructor

class NewClass:

    def __init__(self, num):
        self.num = num

nc = NewClass(2)
print(nc.num)

2

str(nc)

'<__main__.NewClass instance at 0x105cdabd8>'

str() constructor

class NewClass:

    def __init__(self, num):
        self.num = num

    def __str__(self):
        return str(self.num)

nc = NewClass(3)

str(nc)

'3'

Accessing characters in a string

s = "interview"

s[1]

'n'

s[-2]

'e'

s[1:4]

'nte'

s[2:]

'terview'

s[:3]

'int'

The .index() method

s = "interview"

s.index('n')

1

s.index('i')

0

Strings are immutable

s[0] = 'a'

TypeError

 

.capitalize()
.lower()
.upper()
.replace()

Methods return a new string object

Modifying methods 1

# String concatencation
s1 = "worm"
s2 = s1 + "hole"
print(s2)

wormhole

# Replace a substring
s1 = 'a dog ate my food'
s2 = s1.replace('dog', 'cat')
print(s2)

a cat ate my food

Modifying methods 2

# Upper case
s3 = s2.upper()
print(s3)

A CAT ATE MY FOOD

# Lower case
s4 = s3.lower()
print(s4)

a cat ate my food

# Capitalization
s5 = s4.capitalize()
print(s5)

A cat ate my food

Relation to lists

Create a string from a list of strings:

l = ['I', 'like', 'to', 'study']

s = ' '.join(l)
print(s)

I like to study

Breaking a string into a list of strings:

l = s.split(' ')
print(l)

['I', 'like', 'to', 'study']

String methods with DataFrames

import pandas as pd

d = {'name': ['john', 'amanda', 'rick'], 'age': [35, 29, 19]}
D = pd.DataFrame(d)
print(D)

     name   age
0    john    35
1  amanda    29
2    rick    19

String methods with DataFrames

D['name'] = # we will modify this column

String methods with DataFrames

D['name'] = D['name']

String methods with DataFrames

D['name'] = D['name'].str

String methods with DataFrames

D['name'] = D['name'].str.capitalize()

print(D)

     name   age
0    John    35
1  Amanda    29
2    Rick    19

Let's practice!

Practicing Coding Interview Questions in Python