在python中使用递增的字母/数字创建特定大小的文件。

Question

How to create a file of a specific size (say 1024bytes) and each line should have a number or alphabet in an incrementing order. The total size of the file should not exceed 1024 bytes(even after putting alphabets/numbers in it).

I tried this

def create_file_numbers(filename, size):
    f=open(filename,"wb")
    for x in range(size):
        f.write(str(x))
        f.write('\r\n')
    f.close()
    pass

But this creates a file of size much greater than 1024 having numbers 1 to 1023.
I am a beginner in python so explanation would be appreciated.

Answer 1

A string representation of a number is larger than just the number, typically one, two, or four bytes for each character. Your \\r and \\n take up that space too.

max_len = max_size / bytes_per_char
s = ''
i = 0
while len(s) < max_len:
    s += str(i) + '\r\n'
    i += 1
if len(s) > max_len: # because it may not divide evenly
    s = s[:max_len]
open(filename, "wb").write(s)

Answer 2

Define your string of characters:

import string
alphabet = string.digits + string.ascii_letters

Then replace:

f.write(str(x))

with:

f.write(alphabet[x % len(alphabet)])

For example:

>>> import string
>>> alphabet = string.digits + string.ascii_letters
>>> ' '.join(alphabet[x % len(alphabet)] for x in range(200))
'0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 a b c d e f g h i j k l m n o p q r s t u v w x y z A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 0 1 2 3 4 5 6 7 8 9 a b c d'

Answer 3

The only tricky thing about this is that numbers have increasing numbers of digits as they get larger. You can avoid that by padding with zeroes to make each line the same size. For example, let's make each line 8 bytes long. The '\\r\\n' takes up two, leaving 6 for the digits, and that's more than enough.

for n in range(1024/8):
    f.write('%06d\r\n' % n)

To get exactly 1024 bytes without padding, you won't be able to start at 0 or 1. A line with a single digit takes three bytes, two digits takes four bytes, and three digits takes five. 1024 / 5 = 204 remainder 4, so you want 204 lines with three-digit numbers and one with a two-digit number. The two-digit number has to be 99 so that the next number will have three digits. So this works:

for n in range(99, 304):
    f.write('%d\r\n' % n)