How can I remove element from list?

Question

Attempts to remove characters from the string that are not numbers. Unfortunately, I cannot do this due to a reason. I also tried "del file[i][j]", unfortunately without.

Code:

file_open = open("napisy.txt","r")
wyniki = open("wyniki4.txt","w")
file = file_open.read().split()
file1 = file
print(file)
cyfry = ['0','1','2','3','4','5','6','7','8','9']
cyfry_zad3 = ''
licznik_cyfr = 0
tab = []
for i in range(0,len(file1)):
    for j in range(0,len(file1[i])):
        if file1[i][j] not in cyfry:
            file1.remove(file1[i][j])
            #del file1[i][j]
print(file1)

result

Answer 1

How about making it all simpler?

bad_characters = ['0','1','2','3','4','5','6','7','8','9'] 
file_text = file.read()
file_text = ''.join(filter(lambda c: c not in bad_characters, file_text))

A novice-friendly version:

bad_characters = ['0','1','2','3','4','5','6','7','8','9'] 
file_text = file.read()
good_text = ""
for character in file_text:
    if character not in bad_characters:
        good_text += character 
print(good_text)

Answer 2

You can use this

file_open = open("napisy.txt","r")
file = file_open.read()
file_open.close()

for char in list(file):
    if char not in "1234567890":
        file = file.replace(char, "")