Mastering Python Strings notes

String in Python

A string is a sequence of characters enclosed in quotes.

str1 = "Tulasi"
1) Indexing

Access individual characters using index numbers.

Forward Indexing

Starts from 0

T  u  l  a  s  i
0  1  2  3  4  5

Example:

str1[3]

Output:

'a'
2) Negative Indexing

Starts from -1

T   u   l   a   s   i
-6 -5 -4 -3 -2 -1

Example:

str1[-1]

Output:

'i'
3) Length of String

Use len() to find total characters.

len(str1)

Output:

6
String Functions
find()

Returns index if character exists, otherwise returns -1

str1.find("a")

Output:

3

Character not present:

str1.find("k")

Output:

-1
split()

Breaks string into list of words.

text = "hello tulasi"
text.split()

Output:

['hello', 'tulasi']

Used heavily in text processing/NLP.

replace()

Replaces one word with another.

text.replace("tulasi","python")

Output:

'hello python'

Original string remains same unless reassigned.

count()

Counts occurrences of character.

str2 = "Tulasi kumar sahu"
str2.count("a")
Case Sensitive
str2.count("T")
str2.count("t")

Both are treated differently.

Case Conversion Functions
lower()

Converts all characters to lowercase

str2.lower()
upper()

Converts all characters to uppercase

str2.upper()
swapcase()

Lower → Upper
Upper → Lower

str2.swapcase()
title()

Capitalizes first letter of every word

str3.title()
capitalize()

Capitalizes only first letter of full sentence

str3.capitalize()
String Slicing

Syntax:

string[start:end:step]
Normal slicing
str1[0:3]

Output:

'Tul'

End index is not included.

Skip characters
str1[0:6:2]

Output:

'Tls'

Shortcut:

str1[::2]
Reverse String
str1[::-1]

Output:

'isaluT'
Partial Reverse
str1[:1:-1]

Output:

'isa'