Imagine you need to send a thank-you text message to a thousand customers. Writing a thousand lines of code is clearly not the right way. A loop lets you write the instruction once and say "repeat this for every customer".
Common types#
- for: use it when you know how many times to repeat, or which collection to go through.
- while: keep going as long as a condition holds.
Example#
for name in ["Ali", "Sara", "Reza"]:
print("Hello", name)This loop runs three times, once for each name.
Where it is used#
Showing a store's product list, reading the rows of a spreadsheet, checking all comments to find spam, and hundreds of other tasks are done with loops.
Beware of infinite loops#
If the stopping condition is never met, the loop continues forever and the program freezes or ties up the processor. For example, in a while loop, if you forget to increase the counter, it never ends.
A performance note#
A loop inside a loop can become very slow with large amounts of data. If your program suddenly slows down as data grows, nested loops are the first place to check.