我如何使该程序更有效

Question

This program is a basic encoder in python and I want to see if I can make it more efficient without changing the names of the defined variables. Can someone give me some suggestions?

def encode(pattern, filename): 
  f = open(filename, "rt")
  contents = f.read()
  f.close()
  printNow(contents)

  changes = pattern.split("|")
  for str in changes: 
    printNow("Change "+ str[0] + " to " + str[1])

  newMsg = ""
  for char in contents:
     for change in changes:
       if char == change [0]:
         char = change[1]
     newMsg += char 



  f = open(filename + "encoded", "wt")
  f.write(newMsg)
  f.close()

  f = open(filename + "encoded", "rt")
  printNow(f.read())
  f.close()

encode("ae|ga|s3", "C:\\Users\\Shaun\\Desktop\\Test.txt")

Answer 1

import string


def encode(pattern, filename):
    with open(filename) as f:
        contents = f.read()
    s = string.maketrans(*[''.join(a) for a in zip(*pattern.split('|'))])
    newMsg = contents.translate(s)
    with open(filename + 'encoded', 'rt') as f:
        f.write(newMsg)

Answer 2

使用str.translate()而不是艰难地进行所有替换，然后逐行进行。

Answer 3

First of all you need to consider the option that your algorithm is already good enough. Even if it can be optimized, if your code is part of a bigger program and it only executes during 0.1% of time, for instance, then it will be most probably useless to optimize the code, since the rest of the program will dominate the total execution time.

If you really have a problem in your code, then I would start by analyzing the complexity of your algorithm.

And finally, you could try to find some bottlenecks in your code. For that, I would profile the code with something like python's timeit .

Answer 4

The str.translate() method works well for character substitutions, but here's another fast way I've used that also works for multi-character substitutions:

import re

def encode(pattern, filename): 
  f = open(filename, "rt")
  contents = f.read()
  f.close()
  printNow(contents)

  change_dict = {}
  matches = []
  changes = pattern.split("|")
  for str in changes: 
    printNow("Change "+ str[0] + " to " + str[1])
    change_dict[str[0]] = str[1]
    matches.append(str[0])

  change_re = re.compile("|".join(re.escape(x) for x in matches))

  newMsg = change_re.sub(lambda m: change_dict[m.group(0)], contents)

  f = open(filename + "encoded", "wt")
  f.write(newMsg)
  f.close()

  f = open(filename + "encoded", "rt")
  printNow(f.read())
  f.close()

encode("ae|ga|s3", "C:\\Users\\Shaun\\Desktop\\Test.txt")