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Understanding the For Loop

A for loop in Python is used to iterate over a sequence (like a list, tuple, string, or range) or other iterable objects. It’s a concise way to perform actions on each item in a collection.

Basic Syntax:

Python

for item in iterable:
  # code to be executed for each item

Iterating Over Sequences

Python

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
  print(fruit)

The range() Function

The range() function generates a sequence of numbers.

Python

for i in range(5):
  print(i)  # Output: 0, 1, 2, 3, 4

Key Points

  • The loop variable (e.g., fruit or i) takes on the value of each item in the sequence during each iteration.
  • The loop continues until all items in the sequence have been processed.
  • You can use break to exit the loop prematurely and continue to skip the current iteration.

Common Use Cases

  • Iterating over lists, tuples, and strings.
  • Generating sequences of numbers with range().
  • Processing data from files or other sources.

How does a for loop work?

The for loop iterates through each item in the sequence, assigning it to a loop variable.

Can I use a for loop with strings?

Yes, strings are iterable sequences of characters.

Can I modify a list while iterating over it?

It’s generally not recommended to modify a list while iterating over it. Create a copy if necessary.

Can I use a for loop with a dictionary?

Yes, you can iterate over the keys or values of a dictionary.

What is the enumerate() function?

enumerate() returns both the index and value of each item in a sequence.

How can I improve for loop performance?

Consider using list comprehensions or generator expressions for efficiency.

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