Python For-In

Remember: In Python, 'for' and 'for-in' loops are essentially the same thing. The 'for-in' loop is simply a more descriptive way of expressing a loop that iterates over items in an iterable. The keyword 'in' is used to indicate that the loop will iterate over each item in the specified iterable.

for-in

The 'for' loop in Python is used to iterate over a sequence (such as a list, tuple, string, or dictionary) or other iterable objects. It allows you to execute a block of code multiple times, each time with a different value from the sequence.

Its general syntax is as follows:

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for element in iterable:
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# code block

Breakdown:

1. Iterable: An object capable of returning its members one at a time. This can be a sequence like a list, tuple, string, or a generator, etc.

2. Element: A variable that takes the value of the next item in the iterable for each iteration of the loop.

3. Code block: The indented block of code that gets executed for each iteration of the loop. This is where you put the logic you want to execute repeatedly.

Example of iterating over a list:

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# Python: for-in loop
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my_list = [1, 2, 3, 4, 5]
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for num in my_list:
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print(num)

1
2
3
4
5

You can also use the 'range()' function with the 'for' loop to iterate over a sequence of numbers:

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# Python: for-in loop with range() function
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3
for i in range(5):
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print(i)

0
1
2
3
4

The 'for' loop can also be combined with conditional statements like 'if', 'elif', and 'else' for more complex logic within the loop.

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# Python: find odd or even number
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for num in range(10):
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if num % 2 == 0:
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print(num, "is even")
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else:
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print(num, "is odd")

0 is even
1 is odd
2 is even
3 is odd
4 is even
5 is odd
6 is even
7 is odd
8 is even
9 is odd

Note: The code that is intended to be executed within the loop should be indented properly.

Nested for-in

Nested 'for-in' loops in Python allow you to iterate over multiple sequences or iterables in a nested fashion. This is useful when you need to traverse through elements of a multidimensional structure, such as a list of lists or a matrix.

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# Python: for-in loop to print matrix vnumbers
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matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
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for row in matrix:
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for element in row:
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print(element, end=" ")
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print() # Print a newline after each row

1 2 3 
4 5 6 
7 8 9 

In this example, we have a matrix represented as a list of lists. The outer loop iterates over each row of the matrix, and the inner loop iterates over each element within that row. We print each element followed by a space, and after each row, we print a newline character to move to the next line.

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