Python要求用户输入没有换行符？

Question

I just started python a few days ago and have been working on a calculator (not extremely basic, but also not advanced). The problem doesn't prevent code from running or anything, it is just a visual thing. Output in the console looks like this (stuff in parenthesis is explaining what is happening and is not actually part of the output):

4 (user prompted for first number, press enter afterwards)
+ (user prompted for an operator, press enter afterwards
5 (user prompted for second number, press enter afterwards)
9.00000 (answer is printed)

Process finished with exit code 0

Basically what I want it to look like is this when I'm entering it into the console:

4+5
9.00000

I don't want it to start a newline after I enter a number or operator or whatever, it looks more like an actual calculator when it prints along one line. Is this possible to do and if so how? Btw I know end="" works with print but not with input since it doesn't accept arguments. Also I know the whole calculator thing is kind of redundant considering you can make calculations really easily in the python IDLE but I thought it was a good way for me to learn. Here is the entire code if you need it:

import math

while True:
    try:
        firstNumber = float(input())
        break
    except ValueError:
        print("Please enter a number...   ", end="")
while True:
    operators = ['+', '-', '*', '/', '!', '^']
    userOperator = str(input())
    if userOperator in operators:
        break
    else:
        print("Enter a valid operator...   ", end="")
if userOperator == operators[4]:
    answer = math.factorial(firstNumber)
    print(answer)
    pause = input()
    raise SystemExit
while True:
    try:
        secondNumber = float(input())
        break
    except ValueError:
        print("Please enter a number...   ", end="")
if userOperator == operators[0]:
        answer = firstNumber + secondNumber
        print('%.5f' % round(answer, 5))
elif userOperator == operators[1]:
        answer = firstNumber - secondNumber
        print('%.5f' % round(answer, 5))
elif userOperator == operators[2]:
        answer = firstNumber * secondNumber
        print('%.5f' % round(answer, 5))
elif userOperator == operators[3]:
        answer = firstNumber / secondNumber
        print('%.5f' % round(answer, 5))
elif userOperator == operators[5]:
        answer = firstNumber ** secondNumber
        print('%.5f' % round(answer, 5))
pause = input()
raise SystemExit

Answer 1

Your problem is that you're asking for input() without specifying what you want. So if you take a look at the first one: firstNumber = float(input()) It's executing properly, but you hit enter it gives an error which is only then you're specifying what you want.

Try replacing with these:

...
try
    firstNumber = float(input("Please enter a number...   "))
...
    userOperator = str(input("Enter a valid operator...   "))
...
    secondNumber = float(input("Please enter a number...   "))

Is that what you're looking for?

Using my method I suggested:

Please enter a number...   5
Enter a valid operator...   +
Please enter a number...   6
11.00000

Using your method:

Please enter a number...   5

Enter a valid operator...   +

Please enter a number...   6
11.00000

Extra newlines which is what I'm assuming you're referring to.

Answer 2

That's a nice exercise , and as I wrote in the comments, I would ignore whitespaces, take the expression as a whole from the user and then parse it and calculate the result. Here's a small demo:

def is_number(s):
    try:
        float(s)
        return True
    except ValueError:
        return False


def calc(expr):
    if is_number(expr):
        return float(expr)    
    arr = expr.split('+')
    if len(arr) > 1:
        return sum(map(calc, arr))
    arr = expr.split('-')
    if len(arr) > 1:
        return reduce(lambda x,y: x-y, map(calc, arr))
    arr = expr.split('*')
    if len(arr) > 1:
        return reduce(lambda x,y: x*y, map(calc, arr), 1)
    arr = expr.split('/')
    if len(arr) > 1:
        return reduce(lambda x,y: x/y, map(calc, arr))


print calc("3+4-2 *2/ 2")    # 5