使用 for 遍历列表不是从索引开始

Question

I have a list of primes that I am importing from a text file. When I iterate through the list with for, it starts at the third member, but when I use a while loop this problem doesn't occur. My code so far is this:

with open("primes.txt", "r") as f:
    primes = list(f)

primes = [int(i) for i in primes]

z = 0

while z < 10:              #here it starts printing "2,3,5,7,11,..."
    print(primes[z])
    z += 1

for x in primes:           #here it starts printing "5,7,11,..."
    print(primes[x])

I want to know why this happens, if there's a problem when creating the list or if there's any way to fix it.

Answer 1

Here you iterate over z, which starts at 0, so its prints the primes correctly, since the first prime (primes[0]) is 2

while z < 10:              #here it starts printing "2,3,5,7,11,..."
print(primes[z])
z += 1

In the second Block you iterate over the actual prime numbers, so the first print contains primes[2]. So it starts with the 3rd prime number.

for x in primes:           #here it starts printing "5,7,11,..."
print(primes[x])

Answer 2

在第二个循环中，您需要说print(x)而不是print(primes[x]) 。

Answer 3

with open('primes.txt', 'r') as f:
# size_to_read = 100
f_content = f.readlines()
print(f_content)
primes = [int(i) for i in f_content]
# f.close()
for prime in primes:
    print(prime)
f.close()

There exists a method in python called .readlines() that you can apply on file objects and it returns a list for you of all lines in your text file. Happy to help!