如果 x 存在，为什么会发生“ValueError: list.remove(x): x not in list”？

Question

This is a code that opens a table .csv and read line per line to save data in two variables, saved in a list. Moreover, I want to filter some data of sheet (.csv) because I don't need it, and I'm filtering applying what is below, there is, x.remove(i) and y.remove(i) but they both are in error as i reported in the title. What should i do? What mistake am i doing?

g=float(9.8)

x=[]
y=[]

dados = open('dados123.csv').readlines() #trocar para o nome_do_arquivo após testes de diagnóstico



def adiciona_dados():
    for i in range (len(dados)):
        if i !=0:  
            linha = dados[i].split(";")
            x.append(float(linha[0]))
            y.append(float(linha[1])*g)
        else:
            print('erro1')

len(x)
len(y)
adiciona_dados()



for i in y:  
    if y[i] < 30:

        x.remove(i)
        y.remove(i)              
    else:
        print('nada')

len(x)
len(y)

Answer 1

Orignal code:

for i in y:  
    if y[i] < 30:

        x.remove(i)
        y.remove(i)              
    else:
        print('nada')

Modified code version1:

for i in y:  
    if i < 30:

        x.remove(i)
        y.remove(i)              
    else:
        print('nada')

Otherwise,Python list method remove() searches for the given element in the list and removes the first matching element. But if two adjacent elements are repeated, it will remove first one and the second will be reserved.

Modified code version2 for repeated num:

for i in y:
    if i < 30:
        while x.count(i)>0:
            x.remove(i)
        while y.count(i)>0:
            y.remove(i)
    else:
        print("nada")

Answer 2

Welcome to Stack Overflow. We didn't have an example of your dadoos123.csv file. But we can try to understand what your were trying to do. Here's my solution for your problem:

import csv

g = 9.80

with open('dados123.csv', newline='') as dados_file:
    dados_reader = csv.reader(dados_file, delimiter=';')
    print('erro1')
    all_linha = list(dados_reader)
    x = [float(current_linha[0]) for current_linha in all_linha[1:] if float(current_linha[0]) >= 30]
    y = [float(current_linha[1]) * g for current_linha in all_linha[1:] if float(current_linha[0]) >= 30]

how_many_nada = (len(all_linha) - 1) - len(x)     # Could also been (len(all_linha) - 1) - len(y). No difference
for current_nada in range(how_many_nada):
    print('nada')

Is that what you were trying to do?