In Python, using a for loop with the range() function is a common way to control the number of loops. 1. Used when you know the number of loops or need to access elements by index; 2. range(stop) from 0 to stop-1, range(start, stop) from start to stop-1, range(start, stop, step) add step; 3. Note that range does not contain the end value, and returns iterable objects instead of lists in Python 3; 4. You can convert to a list through list(range()) and use negative step size in reverse order.
Using for loops in Python with range() function is one of the most common and practical ways to control the number of loops. If you need to repeat a piece of code to be executed for a fixed number, or iterate through a sequence of numbers, it is very suitable to use for i in range(...) .
When should I use for loop with range()
When you know exactly how many times you want to loop, or you need to access elements by index, it is suitable to use for and range() to cooperate. For example, print numbers from 1 to 10, traverse each position of the list, repeat a certain action N times, etc.
Unlike while loops that rely on conditional judgment, range() can directly generate a sequence of numbers, allowing the loop to run a specified number naturally.
Basic usage and parameter meaning of range()
The three most common ways to write range() are as follows:
-
range(stop): starts at 0 and ends atstop - 1 -
range(start, stop): start fromstart, tostop - 1 -
range(start, stop, step): Add step control
To give a simple example:
for i in range(5):
print(i)The output is 0 to 4, not 5.
Let’s take a look at an example with a starting value and a step size:
for i in range(2, 10, 2):
print(i)2, 4, 6, and 8 will be printed.
Note:
range()does not include the end value (exclusive), which many people are prone to mistakes at the beginning.
How to use it in actual scenarios
Print content with fixed number of times
For example, if you want to print "Hello World" 3 times:
for _ in range(3):
print("Hello World") Here, the variable name is written as _ is a convention, which means that we do not care about specific values.
Traversing the index of the list
If you want to know their location while operating on elements, you can use range(len(list)) :
fruits = ["apple", "banana", "cherry"]
for i in range(len(fruits)):
print(f"The {i} fruit is {fruits[i]}")Control step size to process data
For example, take a value every other element:
numbers = [10, 20, 30, 40, 50]
for i in range(0, len(numbers), 2):
print(numbers[i])This will print 10, 30, 50.
Common misunderstandings and precautions
Forgot range does not contain end value
range(1, 5)is actually 1, 2, 3, 4, not 1 to 5.I mistakenly thought that range returns a list
In Python 3,range()returns a "itable object", not a real list. If you really need a list, you can convert it manually:list(range(5)) # [0, 1, 2, 3, 4]
The situation where the step size is negative
If you want to loop backwards, remember to start to be larger than stop and set a negative step:for i in range(5, 0, -1): print(i)This prints 5 to 1.
Basically that's it. Although it seems simple, mastering the usage of
range()will save you a lot of trouble when writing loop logic.The above is the detailed content of Python for loop range. For more information, please follow other related articles on the PHP Chinese website!
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