String Handling in Python

Master string manipulation, slicing, methods, and formatting techniques in Python

Introduction to Strings

Strings in Python are sequences of characters used to store and manipulate text. Python provides powerful tools for working with strings, including various formatting methods, slicing techniques, and built-in string methods.

Getting String Input

The input() function always returns strings by default:

variable1 = input("Ingrese el valor de la variable 1: ")
variable2 = input("Ingrese el valor de la variable 2: ")

print(f"Valor de variable1: {variable1}, Tipo: {type(variable1)}")
print(f"Valor de variable2: {variable2}, Tipo: {type(variable2)}")

The input() function always returns a string, even if the user enters numbers. To work with numeric input, you must explicitly convert it using int() or float().

String Formatting Methods

Python offers multiple ways to format and display strings. All methods are valid - choose based on your preference and use case.

1. Comma Separation

print(variable1, variable2)

2. String Concatenation

print(variable1 + variable2)

3. format() Method

print("variable1: {} variable2: {}".format(variable1, variable2))

4. F-strings (Recommended)

print(f"{variable1} {variable2}")

F-strings (formatted string literals) are the most modern and readable way to format strings in Python 3.6+.

String Slicing

String slicing allows you to extract portions of a string using index notation [start:end:step].

texto = "ABCDEFGHIJKLMNOP"

# Single character
fragmento = texto[2]
print(fragmento)  # C

# From start to index 5 (excluding 5)
fragmento = texto[:5]
print(fragmento)  # ABCDE

# From index 2 to 5 (excluding 5)
fragmento = texto[2:5]
print(fragmento)  # CDE

# Every second character
fragmento = texto[::2]
print(fragmento)  # ACEGIKMO

# Reverse the string
fragmento = texto[::-1]
print(fragmento)  # PONMLKJIHGFEDCBA

# From index 2 to 10, every second character
fragmento = texto[2:10:2]
print(fragmento)  # CEGI

Slicing syntax: string[start:end:step]

• start: Starting index (inclusive)
• end: Ending index (exclusive)
• step: Increment between characters

String Search Methods

The in Operator

Check if a substring exists within a string:

texto = "hola mundo como estas"
if "mundo" in texto:
    print("la palabra clave esta dentro del texto")

index() Method

Find the position of a substring:

texto = "hola mundo como estas"

# Find "mundo"
print(texto.index("mundo"))  # 5

# Start searching from index 5
print(texto.index("a", 5))  # 20

# Search between index 5 and 8
print(texto.index("a", 5, 8))  # Error if not found

rindex() Method

Search from right to left:

texto = "hola mundo como estas"

# Find last occurrence of "o"
print(texto.rindex("o"))  # 16

# Search up to index 10
print(texto.rindex("o", 0, 10))  # 9

# Search between indices 5 and 15
print(texto.rindex("o", 5, 15))  # 12

String Transformation Methods

Case Conversion

texto = "hola mundo como estas"

# Convert to uppercase
print(texto.upper())  # HOLA MUNDO COMO ESTAS

# Convert to lowercase
texto = "HOLA MUNDO"
print(texto.lower())  # hola mundo

# Capitalize first letter
texto = "hola mundo"
print(texto.capitalize())  # Hola mundo

# Title case (capitalize each word)
texto = "hola mundo"
print(texto.title())  # Hola Mundo

# Swap case
texto = "HoLa MuNdO"
print(texto.swapcase())  # hOlA mUnDo

String Analysis Methods

# Count character occurrences
texto = "anita lava la tina"
print(texto.count("la"))  # 2

# Get string length
texto = "hola mundo como estas"
print(len(texto))  # 21

String Validation Methods

startswith() and endswith()

texto = "hola mundo"

# Check if starts with substring
print(texto.startswith("hol"))  # True

# Check if ends with substring
print(texto.endswith("do"))  # True

isdigit()

texto = "2455"
print(texto.isdigit())  # True

texto = "24a55"
print(texto.isdigit())  # False

Use isdigit() to validate numeric input before converting strings to integers.

String Modification Methods

replace()

Replace substrings:

texto = "hola mundo"
print(texto.replace("mundo", "familia"))  # hola familia

strip()

Remove leading and trailing whitespace:

cadena = "   ¡Hola, mundo!   "
cadena_sin_espacios = cadena.strip()
print(cadena_sin_espacios)  # ¡Hola, mundo!

Related methods: lstrip() removes left whitespace, rstrip() removes right whitespace.

Common String Methods Summary

Method	Description	Example
len()	Get string length	len("hello") → 5
upper()	Convert to uppercase	"hello".upper() → “HELLO”
lower()	Convert to lowercase	"HELLO".lower() → “hello”
capitalize()	Capitalize first letter	"hello".capitalize() → “Hello”
title()	Capitalize each word	"hello world".title() → “Hello World”
count()	Count occurrences	"hello".count("l") → 2
replace()	Replace substring	"hello".replace("l", "r") → “herro”
strip()	Remove whitespace	" hi ".strip() → “hi”
startswith()	Check prefix	"hello".startswith("he") → True
endswith()	Check suffix	"hello".endswith("lo") → True
isdigit()	Check if numeric	"123".isdigit() → True
index()	Find substring position	"hello".index("e") → 1