STRINGS

Strings are one of the most important data types in Python. We use strings whenever we work with names, messages, filenames, database errors, log files, user input, and other text data.

In this tutorial, we will learn Python strings from the absolute basics with simple examples.

Table of Contents

  1. What is a String?
  2. Creating Strings
  3. Finding String Length with len()
  4. Python Functions vs String Methods
  5. upper() and lower()
  6. Removing Spaces with strip()
  7. Replacing Text with replace()
  8. String Immutability
  9. String Indexing
  10. Negative Indexing
  11. String Slicing
  12. Slicing Shortcuts
  13. Slicing with Step
  14. Reversing a String
  15. in and not in
  16. startswith() and endswith()
  17. split()
  18. join()
  19. find()
  20. count()
  21. F-Strings
  22. Common Beginner Mistakes
  23. Quick Revision
  24. Practice Questions

1. What is a String?

A string is text stored in Python.

Examples:

name = "Prabhu"
city = "Hyderabad"
job = "DBA"

In Python, the string data type is called: 

str

2. Creating Strings

Strings can be created using quotes. 

name = "Prabhu"

print(name)
print(type(name))

Output:

Prabhu
<class 'str'>

3. Finding String Length with len()

The len() function returns the number of characters in a string. 

name = "Prabhu"

print(len(name))

Output:

6

Spaces are also counted as characters. 

name = "Prabhu Charan"

print(len(name))

Output:

13

4. Python Functions vs String Methods

Beginners often get confused because both functions and methods use parentheses.

Function

len(name)

The general pattern is:

function(value)

Method

name.upper()

The general pattern is:

object.method()
Easy memory rule:
len(name) → Function
name.upper() → Method

5. upper() and lower()

upper() converts text to uppercase.

lower() converts text to lowercase. 

city = "Hyderabad"

print(city.upper())
print(city.lower())

Output:

HYDERABAD
hyderabad

6. Removing Extra Spaces with strip()

strip() removes spaces from the beginning and end of a string. 

name = "   Prabhu   "

print(name.strip())

Output:

Prabhu

This is especially useful with user input. 

name = input("Enter your name: ")

name = name.strip()

print(f"Hello {name}")

7. Replacing Text with replace()

The replace() method replaces one part of a string with another. 

text = "I like Java"

text = text.replace("Java", "Python")

print(text)

Output:

I like Python

8. Strings are Immutable

One very important Python concept is that strings are immutable.

This means string methods normally create a new string rather than modifying the original string directly. 

name = "prabhu"

name.upper()

print(name)

Output:

prabhu

The result was created, but we did not save it.

To save the new value:

name = "prabhu"

name = name.upper()

print(name)

Output:

PRABHU
Remember:
name.upper() → result created but not saved
name = name.upper() → result created and saved

9. String Indexing

Each character in a Python string has an index position.

Python indexing starts from 0. 

Character:  P  y  t  h  o  n
Index:      0  1  2  3  4  5

Example:

name = "Python"

print(name[0])
print(name[1])
print(name[2])

Output:

P
y
t

10. Negative Indexing

Python can also count backwards from the end of a string. 

Character:       P   y   t   h   o   n
Positive Index:  0   1   2   3   4   5
Negative Index: -6  -5  -4  -3  -2  -1

Example:

name = "Python"

print(name[-1])
print(name[-2])

Output:

n
o

11. String Slicing

Slicing allows us to extract multiple characters from a string.

The syntax is:

string[start:stop]

The start position is included, but the stop position is excluded. 

text = "Database"

print(text[0:4])

Output:

Data

text[0:4] takes indexes: 

0, 1, 2, 3

Index 4 is not included.

12. Slicing Shortcuts

text = "Database"

print(text[:4])
print(text[4:])
print(text[:])

Output:

Data
base
Database

Remember:

text[:4]  → beginning to before index 4

text[4:]  → index 4 to the end

text[:]   → entire string

13. Slicing with Step

The full slicing syntax is:

string[start:stop:step]

Example:

text = "Database"

print(text[::2])
print(text[1::2])

Output:

Dtbs
aaae

14. Reversing a String

We can reverse a string using a step value of -1. 

text = "Python"

print(text[::-1])

Output:

nohtyP

15. Checking Text with in and not in

The in operator checks whether something exists inside a string. 

text = "PostgreSQL Database"

print("SQL" in text)
print("Oracle" in text)

Output:

True
False

not in checks whether something is absent. 

print("Oracle" not in text)

Output:

True
Python string comparisons are case-sensitive.

"Python" and "python" are different.

16. startswith() and endswith()

startswith() checks the beginning of a string.

endswith() checks the end. 

filename = "backup.sql"

print(filename.startswith("backup"))
print(filename.endswith(".sql"))
print(filename.endswith(".csv"))

Output:

True
True
False

Practical Example

filename = input("Enter file name: ")

if filename.endswith(".csv"):
    print("CSV file")
else:
    print("Not a CSV file")

17. Splitting Strings with split()

split() breaks one string into multiple pieces. 

text = "apple,banana,mango"

result = text.split(",")

print(result)

Output:

['apple', 'banana', 'mango']

The result of split() is a Python list.

Another example:

data = "Prabhu|DBA|Hyderabad"

result = data.split("|")

print(result)

Output:

['Prabhu', 'DBA', 'Hyderabad']

18. Joining Strings with join()

join() performs the opposite operation of split(). 

words = ["Python", "is", "easy"]

result = " ".join(words)

print(result)

Output:

Python is easy

Different separators can be used:

print("-".join(words))
print(",".join(words))

Output:

Python-is-easy
Python,is,easy
Easy comparison:

split() → one string becomes many pieces
join() → many string pieces become one string

19. Finding Text with find()

find() returns the index where some text starts. 

text = "Python is easy"

print(text.find("easy"))

Output:

10

If the value cannot be found, find() returns -1. 

print(text.find("Java"))

Output:

-1

20. Counting Occurrences with count()

count() tells us how many times something appears. 

text = "banana"

print(text.count("a"))

Output:

3

Remember the difference:

find()  → WHERE does it start?

count() → HOW MANY times does it occur?

21. F-Strings

F-strings are one of the cleanest ways to combine text and variables. 

name = "Prabhu"
experience = 10

print(f"My name is {name}")
print(f"I have {experience} years of experience")

Output:

My name is Prabhu
I have 10 years of experience

Python can also evaluate expressions inside an f-string. 

experience = 10

print(f"Next year I will have {experience + 1} years of experience")

Output:

Next year I will have 11 years of experience

22. Common Beginner Mistakes

Mistake 1: Forgetting that indexing starts from 0

text = "Python"

print(text[0])

Output is P, because the first index is 0.

Mistake 2: Including the stop index in slicing

text[0:3]

This uses indexes:

0, 1, 2

Index 3 is excluded.

Mistake 3: Forgetting to save a changed string

name.upper()

This does not permanently change name.

Use:

name = name.upper()

Mistake 4: Forgetting case sensitivity

"Python" != "python"

Mistake 5: Confusing find() and count()

find()  → position

count() → number of occurrences

23. Quick Revision

Operation Purpose
len(text) Number of characters
text.upper() Uppercase
text.lower() Lowercase
text.strip() Remove outside spaces
text.replace() Replace text
text[0] First character
text[-1] Last character
text[0:4] Slice text
text[::-1] Reverse string
"SQL" in text Check presence
text.startswith() Check beginning
text.endswith() Check ending
text.split() String to pieces
" ".join(words) Pieces to string
text.find() Find starting index
text.count() Count occurrences
f"{name}" Insert variable into text

24. Practice Questions

Try these exercises without looking at the answers first.

Exercise 1

text = "Python"

print(text[0])
print(text[-1])
print(text[::-1])

Exercise 2

text = "Database"

print(text[:4])
print(text[4:])

Exercise 3

filename = "backup.sql"

print(filename.endswith(".sql"))
print(filename.startswith("backup"))

Exercise 4

data = "PostgreSQL|MySQL|Redshift"

result = data.split("|")

print(result)

Exercise 5

text = "database database python"

print(text.count("database"))
print(text.find("python"))

Conclusion

Python strings are extremely important because almost every real-world Python application works with text in some form.

In this tutorial we learned how to create strings, change case, remove spaces, replace text, access characters, perform slicing, search strings, split and join text, count values, and use f-strings.

The next topic in our Python learning roadmap is:

Python Lists

Lists allow us to store multiple values inside a single variable.

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