Python 3：使用变量执行for循环x次

Question

Edit: Fixed the screwed up brackets, sorry. Should have caught this. Let's see if this clarifies what I'm trying to do.

I want to do a basic program that takes the variable "run" and runs the following code that number of times by using a For loop.

run = 3
def program(run):
    for i in range(5):
        print("The number is",i)

program(run)

What I want is to get is:

the number is 0
the number is 1
the number is 2
the number is 3
the number is 4
the number is 0
the number is 1
the number is 2
the number is 3
the number is 4
the number is 0
the number is 1
the number is 2
the number is 3
the number is 4

ie the "program" loops however many times I set "run" to equal.

Answer 1

Let's break the code and the error message down a bit:

    for i in range[5]:
TypeError: 'type' object is not subscriptable

"Subscripting" is the way you access a particular element in a container, like a list or a dict. For example, to get the first (0th) element of a list called foo , you'd say foo[0] , and to get the value associated with the key "bar" in a dictionary called foo , you'd say foo["bar"] .

Note that when you just use the [] symbols by themselves (instead of putting them after some other identifier), they serve a different purpose: they construct a list . The expression [5] is a list that contains a single element (the number 5 ). To represent more elements, you comma-separate them, eg [0, 1, 2, 3, 4] .

So what the error is telling you is that a type object can't be subscripted. Does that mean that range is a type ? Yes! In Python, a range is a type of iterable object that represents a range of numbers. On its own, the word range in a Python program refers to the entire class of range objects (that is, a type of object), not a particular range object.

You construct a range the same way you construct most objects, by calling the type as a constructor function, with parameters in parentheses. For example, to construct a range with 5 numbers in it (0 to 4, similar to the list [0, 1, 2, 3, 4] ) you can simply say range(5) .

So to print all the numbers from 0 to 4 you can do:

    for i in range(5):
        print("The number is", i)

In your code, the run variable serves no purpose and can be removed completely. Functions can take any number of parameters, or none at all, and since in this case your function doesn't do anything with the parameter you pass in, it can be simply:

def program():
    for i in range(5):
        print("The number is", i)

program()

If you wanted to make the length of the range variable, that would make sense as a parameter -- you just need to pass the parameter along to your range construction:

def program(num):
    for i in range(num):
        print("The number is", i)

runs = 3
for _ in range(runs):
    program(5)

Answer 2

You'd use range, but you would use parenthesis to call the function instead of braces. Ie range(5) instead of range[5] . Or you could use your run variable like range(run)

Answer 3

In short you are seeing the error because you are using square brackets and not parentheses range() is a function. Change it to

def program(run):
    for i in range(5):
        print("The number is",i)

program(run)
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4

and it works fine.

If you want to the program to loop the same number of times as specified in run then you can do this:

run = 5
def program(run):
    for i in range(run):
        print("the number is",i)

program(run)

Answer 4

def program(n):
    for i in range(0,n+1):
        print("The number is",i)

program(5)

ouput

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
The number is 5

Answer 5

Whelp, I finally figured it out - the reason I couldn't seem to find a solution anywhere to "could this be done and how would I go about it" is that in Python at least, a For statement cannot do this kind of loop, only a While can.

So my experiment of trying to do this via a For is a moot point, it's not something that can be coded without using While.

Thanks for the help.

Answer 6

Give this a try. Hopefully understood the assignment:

run = 3


def program(run):
    nums = [f'The number is: {n}' for r in range(run) for n in range(5)]
    print('\n'.join(nums))

program(run)

This uses list comprehension to loop twice which translates to:

run = 3


def program(run):
    for r in range(run):
        for n in range(5):
            print(f'The number is: {n}')

program(run)

Or:

run = 3


def program():
    for n in range(5):
        print(f'The number is: {n}')

for r in range(run):
    program()

Output:

The number is: 0
The number is: 1
The number is: 2
The number is: 3
The number is: 4
The number is: 0
The number is: 1
The number is: 2
The number is: 3
The number is: 4
The number is: 0
The number is: 1
The number is: 2
The number is: 3
The number is: 4