At the start sorry for my english. I wrote some code in PyCharm where i'am trying to divide string with mathematical operators such as +,-, itp and numbers but at the same time saving position of the mathematical operators and what they were.
string = '1234 - 4332 / 23 + 13 + 12 + 3213'
znaki = []
znakik = []
ilznak = string.count('+')+string.count('-')+string.count('/')+string.count('*')
i = [0,0,0,0]
num = string.split(" ")
print(num)
x = len(num)
while num.count('+')+i[0] >= i[0]:
znaki.append('+')
znakik.append(num.index('+'))
print(znakik)
num.pop(num.index('+'))
i[0] = i[0] + 1
print(num)
It's work sometimes but sometimes it gives me error :
Traceback (most recent call last):
File "D:/Prog/Python/Działaniastring.py", line 11, in <module>
znakik.append(num.index('+')+i[0])
ValueError: '+' is not in list
Why is it that it pops sometimes but not always and what causes it?
Welcome to Stackoverflow. As a beginner in python you should definitely consider using python visualizer to understand the entire logic of the code. see here
Running your code gives this output:
['1234', '-', '4332', '/', '23', '+', '13', '+', '12', '+', '3213']
[5]
['1234', '-', '4332', '/', '23', '13', '+', '12', '+', '3213']
[5, 6]
['1234', '-', '4332', '/', '23', '13', '12', '+', '3213']
[5, 6, 7]
['1234', '-', '4332', '/', '23', '13', '12', '3213']
And clearly when there remains no more '+' you would get the error that
ValueError: '+' is not in list
So how does this happen?
1 znakik.append(num.index('+'))
2 num.pop(num.index('+'))
In line 2 you pop the '+' from the array on each iteration, i,e. the index value stored in the znkakik array. Once you do this for all you end up with no more '+', and then the error.