PYTHON3：如何打印出用户输入的字符串并以逗号分隔打印出来？

Question

My current code is:

def my_input(): 
    my_string = input("Important ions are: ")
    for i in my_string:
        print(my_string, sep=",")

my_input()

So I am trying to write a program, whereby the user is prompted "Important elements are:" and is expected to input:

Na K Ca Mg Mn(all on one line separated by single spaces):

Then, I want my code to print out the following:

Important ions are: Na, K, Ca, Mg and Mn

Instead, with my current code, I am getting the following output:

Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn
Na K Ca Mg Mn

I am confused as to why/how this is the output printed that many times. I think I get why it is not being separated by a comma, is it because it is treating the input as 1 string? And I guess in order to print out my desired output, I'd have to do like

print("Important ions are" + my_string)

But I know that cannot be correct and then how could I get to print out the input, separated by commas and add an "and" in between as the desired output displayed above??

Answer 1

First, your guess is right, you have to add the string "Important ions are" when you print your output.

Besides, you used 'my_string' (all ions input) in your for-loop, that's why you get 'Na K Ca Mg Mn' printed for multiple times.

What you need will look like this

def my_input(): 
    my_string = input("Important ions are: ")
    ions = my_string.split(' ')
    print("Important ions are: ", end='')
    for j, i in enumerate(ions):
        if j == 0:
            print(i, end='')
        if j == (len(ions) - 1):
            print(' and ' + i)
        else:
            print(', ' + i, end='')

my_input()

---

Output:

# >>> my_input()
# Important ions are: Na K Ca Mg Mn
# Important ions are: Na, Na, K, Ca, Mg and Mn

Answer 2

Here is an alternative version

def my_input(): 
    my_string = input("Important ions are: ")
    ions = my_string.split() # Split input by whitespace characters
    print('Important ions are:', ', '.join(ions))

my_input()

• ions stored a list of the input ions.
• ', '.join(ions) returns a string of ions separated by a comma followed by a space.
• print is used to print the prefix Important ions are: and the joined string. Note that print use a space to separate the given arguments.

---

To show and between the last two item, the last item should be printed separately. Here is the updated version.

def my_input(): 
    my_string = input("Important ions are: ")
    ions = my_string.split() # Split input by whitespace characters
    print('Important ions are:', ', '.join(ions[:-1]), 'and', ions[-1]))

my_input()

• ions[:-1] : slicing the ions list up to the second last item.
• ions[-1] : the last item.

See slicing on Python tutorial .

However, the code will produce strange result or errors if only one ion or no ion is entered, respectively. To fix the issue, the length of the ions should be assesed:

def my_input(): 
    my_string = input("Important ions are: ")
    ions = my_string.split() # Split input by whitespace characters
    if len(ions) > 1:
        print('Important ions are:', ', '.join(ions[:-1]), 'and', ions[-1]))
    elif lrn(ions) == 1:
        print('Important ion is:', ions[0])
    else:
        print('No ions are important')
my_input()

Answer 3

You could try this:

import re
def my_input(): 
    my_string = input("Important ions are: ").split()   # storing the input as elements of a list
    w = " ".join(my_string)                                     # joining all the elements in the list  
    print("Important ions are: ", re.sub(" ",", ",w[0:-2]) +'and '+ my_string[-1])  # appending the last element after inserting ', ' and 'and'

my_input()

This should give you the output exactly the way you wanted. The reason why your code prints the input repeatedly is because of this line:

 print(my_string, sep=",")

It just prints the whole input as many times as there elements in the input. Also, sep= "," won't work in loops.