For loops are fundamental programming constructs that enable developers to create iteration in their code while automating repetitive tasks effectively. Python offers a clean and straightforward syntax to implement for loops, making your code more readable. In this tutorial, we’ll discuss how to start a for loop in Python, including relevant concepts like the range function and list comprehensions.
Step 1: Basic Syntax of For Loop
The general syntax for a for loop in Python is:
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for variable in iterable: # code to be executed |
Here, the iterable can be a list, tuple, string, dictionary, or range object. The variable stores the current element in the iterable, and the loop iterates through to the next element until it reaches the end of the iterable.
Step 2: Looping Through Lists
To illustrate the use of a for loop, we’ll create a list and iterate through each item:
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fruits = ['apple', 'banana', 'cherry'] for fruit in fruits: print(fruit) |
The output of the above code will be:
apple banana cherry
Step 3: Using the Range Function in For Loop
In some instances, you might need to iterate over a range of numbers rather than a collection of items. You can use Python’s range() function to generate a range object that is suitable for iterations. The range function takes three arguments: start, stop, and step – where start is inclusive, and stop is exclusive.
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for number in range(start, stop, step): # code to be executed |
Let’s iterate through the numbers from 1 to 10 using the range function:
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for number in range(1, 11): print(number) |
The output of the above code will be:
1 2 3 4 5 6 7 8 9 10
Step 4: Looping Through Strings
You can also iterate through each character of a string using a for loop:
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word = 'python' for letter in word: print(letter) |
The output of the above code will be:
p y t h o n
Step 5: List Comprehensions
Python’s list comprehensions offer a concise way to create new lists by iterating through an iterable and applying specific conditions or actions to each element. The general syntax for list comprehension is:
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[expression for item in iterable if condition] |
Suppose we want to create a list containing the squares of all even numbers from 1 to 10. Using list comprehension, we can achieve that in a single line:
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squares = [number**2 for number in range(1, 11) if number % 2 == 0] print(squares) |
The output of the above code will be:
[4, 16, 36, 64, 100]
Full Code
Here is the full code used in this tutorial:
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# Step 2 fruits = ['apple', 'banana', 'cherry'] for fruit in fruits: print(fruit) # Step 3 for number in range(1, 11): print(number) # Step 4 word = 'python' for letter in word: print(letter) # Step 5 squares = [number**2 for number in range(1, 11) if number % 2 == 0] print(squares) |
Conclusion
Now you have a solid understanding of how to start a for loop in Python, including iterating through various types of iterables and using the range function. With this knowledge, you’re well-equipped to write more efficient, concise, and readable code for your future projects.