请帮助理解 Python 中的代码

Question

I'm trying to polish my python skills and this made me confused. Here's the code:

greeting = 'Hello!'
count = 0

for letter in greeting:
    count += 1
    if count % 2 == 0:
        print(letter)
    print(letter)

print('done')

I don't understand what the count does.

Answer 1

this exact code doubles letters which position number is even. count is for counting letter position. condition count % 2 == 0 to know which position is divided by 2 without leftovers (check if position is even number)

Answer 2

Let's comment up the code with explanations of what each line does and then examine the output.

# assign the string 'Hello!' to the name greeting
greeting = 'Hello!'
# assign the number 0 to the name count
count = 0

# assign letter to each character in greeting one at a time.
# in the first run of the loop, letter would be 'H', then 'e',
# etc.
for letter in greeting:
    # add one to count. count starts at 0, so after this line
    # on the first run of the loop, it becomes 1, then 2, etc.
    count += 1
    # use the modulo operator (%) to get the remainder after
    # dividing count by 2, and compare the result to 0. this
    # is a standard way of determining if a number is even.
    # the condition will evaluate to True at 0, 2, 4, etc.
    if count % 2 == 0:
        # when count is even, print letter once followed by a
        # new line. note that to not print a new line, you can
        # write print(letter, end="")
        print(letter)
    # print letter once followed by a new line regardless of the
    # value of count
    print(letter)

# print 'done' followed by a new line
print('done')

So, based on all that, what should we expect the output to be? Well, we know that every character of greeting will be printed in the last line of the loop. We also know that every even character of greeting will be printed twice, once inside the if block, and once at the end of the loop. Finally, we know that "done" will be printed after the loop is complete. Therefore, we should expect the following output:

H
e
e
l
l
l
o
!
!
done

Answer 3

This this is very simple see:

greeting = 'Hello!'

In this line you assigned the variable greeting a string value Hello! .

count = 0

In this line you assigned the variable count a integer value 0 . Now the next code is:

for letter in greeting:
    count += 1
    if count % 2 == 0:
        print(letter)
    print(letter)

As you may know strings are iterable. See this code before understanding the above:

for letter in greeting:
    print(letter)

Forget the count. At each iteration of the loop the loop is printing every character of the greeting. so the output is:

H
e
l
l
o
!

But why there a newline after each letter. The answer is that print has an optional argument end If the above code is like this:

    for letter in greeting:
       print(letter, end = '')

Then the output will be:

Hello!

Now there comes the count term. It is also simple. when the count is even it prints the letter iterating at that time in loop twice due to twice print statement. And the count is even or not is checked by if count % 2 == 0 .