在文件中遇到空行后重新迭代循环（Python）

Question

基本上，我有一段代码，它会读取一个包含多个段落的文本文件，然后根据每个段落第一行的指示来解码后面的内容。我们的示例看起来是这样的：

-25+122-76
?ST^jT^jLj_P^_jZQj_SPjTY[`_jQTWPx
?ST^jT^j_SPj^PNZYOjWTYPx

+123+12+1234
0A:MXPBEEXA:II>GXGHPw

解码的过程是把第一行的数字相加，然后根据这个数字来移动每个字符的ASCII值。到目前为止，我的代码是这样的：

#Here I define the Shift function that will take a character, convert it to its ASCII numeric value, add N to it and return the ASCII character.

def Shift(char, N):
    A = ord(char)
    A += N
    A = chr(A)
    return A

#Here's the code I have that opens and reads a file's first line as instructions, evaluates the numeric value of that first line, throws rest into a list and runs the Shift helper function to eval the ASCII characters.
def driver(filename):
    file = open(filename)
    line = file.readline()
    file = file.readlines()
    N = eval(line)
    codeList = list(file)  
    for char in codeList:  
        newChar = Shift(char, N)  
        codeList[char] = codeList[newChar]  
    print str(codeList)  

现在我想问的是，如何让我的代码在每个段落的空行后重新开始？还有，怎么让字符的移动只在ASCII范围32（空格）到126（波浪号）之间？另外，我使用的是Python 2.7.3。

Answer 1

为了让数据保持在一个范围内，你可以使用一个叫做 deque 的东西。我还建议你不要用 eval，而是先手动把数字转换成整数，然后再用一个翻译表来解码数据，比如：

data = """-25+122-76
?ST^jT^jLj_P^_jZQj_SPjTY[`_jQTWPx ?ST^jT^j_SPj^PNZYOjWTYPx"""

lines = data.splitlines()

import re
from collections import deque
from string import maketrans

# Insted of using `eval` - find number with signs and sum
shift = sum(int(i) for i in re.findall('[-+]\d+', lines[0]))
# Explicit range of characters
base_set = map(chr, range(32, 127))
# Create a new deque which can be rotated and rotate by shift
d = deque(base_set)
d.rotate(-shift)
# Make translation table and translate
t = maketrans(''.join(base_set), ''.join(d))
print lines[1].translate(t)
# This is a test of the input file.5This is the second line.

Answer 2

file = open(filename)
while True:
    line = file.readline()
    if not line:      # if end of file, exit
        print "Reached end of file"
        break
    if line == "\n":  # if new line, or empty line, continue
        continue
    else:
        your function

关于如何保持所有内容在ASCII范围内，我需要再想想。如果没有快速的答案，可以尝试使用其他控制结构来确保所有内容都在正确的范围内，简单的数学运算应该就能解决这个问题。

你也可以参考这个： 链接