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Python String

Video link: https://youtu.be/GQywwPUrsgA

In this video, we learned about Python strings in depth.

Programs in the Video

Create a String

A string is a sequence of characters or textual data. In Python, we create strings by enclosing characters inside quotations like:

# single quote
text = 'Hello there'
print(text)

# double quotes
text = "Hello there"
print(text)

# triple quotes for multiline strings
text = """Hello there.
How are you doing"""
print(text)

Output

Hello there
Hello there
Hello there.
How are you doing

However, we can't use mismatching quotations like:

# mismatching strings
text = 'Hello there"
print(text)

Output

File "<string>", line 2
    text = 'Hello there"
                       ^
SyntaxError: EOL while scanning string literal

Suppose we want to create a string:

He said, "What's there?"

It contains both single quotes and double quotes, so using either of those would give error:

text =  "He said, "What's there?""
print(text)

Output

File "<string>", line 1
    text =  "He said, "What's there?""
                       ^
SyntaxError: invalid syntax

To fix this, we can escape characters like quotations by using a backslash \ before it.

text =  "He said, \"What\'s there?\""
print(text)

Output

He said, "What's there?"

Access String Characters

A string is a sequence of characters, and these characters are in order. So, we can access individual characters of a string using indices just like with lists and tuples.

text = "Python"
print(text)

Output

Python

Here, every elements in the list maintain an order.

We can access individual characters of string by using its index. Index starts from 0. So the index of the first character is 0, the second character is 1 and so on.

Character Index
'P' 0
'y' 1
't' 2
'h' 3
... ...

We can use indices in the following way:

text = "Python"

# first character
print(text[0])

# fourth character
print(text[3])

Output

P
h

If the specified index does not exist in the string, Python throws an IndexError exception.

text = "Python"
print(text[10])

Output

Traceback (most recent call last):
  File "<string>", line 2, in <module>
IndexError: string index out of range

Negative Indexing

In Python, we can also use negative indexing for sequences like string. Using a negative index gives us characters from the last.

Character Index
'P' -6
'y' -5
't' -4
'h' -3
'o' -2
'n' -1

Negative index can be used like normal index:

text = "Python"

# last character
print(text[-1])

# third to last character
print(text[-3])

Output

n
h

Slicing of a String

It is also possible to access multiple characters from the string, not just a single character.

For example,

text = "Python"

# 2nd, 3rd and 4th characters
print(text[1:4])

Output

yth

While using slicing, the starting index is inclusive but the ending index is exclusive.

Notes:

  • If we use the empty start index, the slicing starts from the beginning of the string.
  • If we use the empty end index, the slicing ends at the last string character.
text = "Python"

# first to fourth characters
print(text[:4])

# from third to last character
print(text[2:])

Output

Pyth
thon

Change and Delete String Characters

Strings in Python are immutable, and we cannot add or change characters of a string. Let's see what happens when we try to change characters of a string:

text = "Python"
text[0] = "p"
print(text)

Output

Traceback (most recent call last):
  File "<string>", line 2, in <module>
TypeError: 'str' object does not support item assignment

Python String Operations

Concatenation

It denotes the joining of two strings into one. To join two strings, we can use the plus + operator.

text1 = "Python"
text2 = "Programming"

result = text1 + " " + text2
print(result)

Output

Python Programming

Repeating strings

We use the asterisk * operator to repeat a string a certain number of times:

text = "Python"
new_text = text * 3

print(new_text)

Output

PythonPythonPython

Iterating through a String

If we want to get individual characters of a string one by one, we can use a for loop.

text = "Python"

for character in text:
    print(character)

Output

P
y
t
h
o
n

In each iteration, the value of character is each individual character from the text string.

We can use len() to find length of a string:

text = "Python"
print(len(text))

Output

6

We can also use the in operator to find out if a substring is present in a given string:

text = "Python"
print("P" in text)

print("yth" in text)

print("ont" in text)

Output

True
True
False

Python String Methods

Strings are probably the most frequently used data type. To make working with strings easier, Python has numerous string methods readily available for us to use.

lower() and upper() method

To make all the characters lowercase, we can use the lower() method.

text = "I like Python 3"
result = text.lower()

print(result)

Output

i like python 3

Similarly, if we want all uppercase characters, we can use the upper() method.

text = "I like Python 3"
result = text.upper()

print(result)

Output

I LIKE PYTHON 3

find() method

To find the index of the Python substring, we can use the find() method.

text = "I like Python 3"
result = text.find("Python")

print(result)

Output

7

replace() method

To replace a substring with another, we can use the replace() method.

text = "I like Python 3"
result = text.replace("Python 3", "Java")

print(result)

Output

I like Java

Programming Task

Can you guess the output of this program?

quote = "Talk is cheap. Show me the code."

print("1.", quote[3])
print("2.", quote[-3])
print("3.", quote.replace("code", "program"))

Output

1. k
2. d
3. Talk is cheap. Show me the program.