Any tips for improving efficiency in general?

Question

I have been doing simple programming challenges all day, trying to learn and practice. I however, always seems to fail at efficiency. Without using built_in code (such as the encode method), is there anyway that I could improve my program's efficiency (my efficiency in general)?

import string
alph = string.ascii_lowercase
def encrypt(text):

    encryption = ""

    for character in text:

        index = 0
        shift = 0
        for letter in alph:                       
            if letter == character:

                if index > 23:
                    shift = abs(26 - (index+3))
                    encryption += alph[shift]
                    break
                shift = index + 3
                encryption += alph[shift]

            index += 1

    return encryption

def decrypt(text):

    decryption = ""

    for character in text:

        index = 0
        shift = 0
        for letter in alph:                       
            if letter == character:

                if index < 3:
                    shift = abs(26 - (index+3))
                    decryption += alph[shift]
                    break
                shift = index - 3
                decryption += alph[shift]

            index += 1

    return decryption

This is currently very broad -- it already would be much better if you'd asked about the efficiency of some construct. You don't define what efficiency is (in writing, runtime performance, ...) for you though, so it's impossible to tell what the correct answer would be. — Benjamin Bannier, Dec 07 '12 at 09:09

score 1 · Answer 1 · edited May 23 '17 at 12:29

You could use slices and str.maketrans, str.translate (see Python.org : string):

import string

def rot3_encode(s):
    return s.translate(
            string.maketrans(
                # 'abcdefghijklmnopqrstuvwxyz'
                string.ascii_lowercase,
                # 'defghijklmnopqrstuvwxyz' + 'abc'
                string.ascii_lowercase[3:] + string.ascii_lowercase[:3] # 
                )
            )

without using translate and maketrans :

def rot3(s):
    # 'abcdefghijklmnopqrstuvwxyz'
    original_alphabet = string.ascii_lowercase 
    # 'defghijklmnopqrstuvwxyz' + 'abc'
    encoded_alphabet = string.ascii_lowercase[3:] + string.ascii_lowercase[:3]
    encoded_string = ''
    for character in s:
        # look at what index your character is in the original alphabet
        encoded_string += encoded_alphabet[original_alphabet.index(character)]
    return encoded_string

for exemple:

rot3('afz')
# 'a' is at index 0 of 'abcdefghijklmnopqrstuvwxyz'
# -> you will append to your encoded string the character at index 0 of 'defghijklmnopqrstuvwxyzabc' ('d')
# 'f' is at index 5 of 'abcdefghijklmnopqrstuvwxyz'
# -> you will append to your encoded string the character at index 5 of 'defghijklmnopqrstuvwxyzabc' ('i')
# ...
>>>'dic'

score 1 · Answer 2 · edited May 23 '17 at 11:55

1

using string formatting "%s%s" (encryption, newvalue) is 2x faster, compared using += and + the difference gets even bigger with larger strings.

see String concatenation vs. string substitution in Python

edited May 23 '17 at 11:55

Community

1
1

answered Dec 07 '12 at 16:18

Stephan

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THAT is interesting to know... +1! – heltonbiker Dec 07 '12 at 16:26

zeffii · Answer 3 · 2012-12-07T10:38:00.177

0

Instead of explicit index += 1 you can for example use for index, letter in enumerate(alph):. This shrinks the code a little and tracks iteration index automatically.

edited Dec 07 '12 at 10:38

answered Dec 07 '12 at 09:03

zeffii

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score 0 · Answer 4 · answered Dec 07 '12 at 09:25

0

Invoking it this way to see where the time is consumed is your most basic tool for improving performance...

 python -m cProfile foo.py

See here for more

answered Dec 07 '12 at 09:25

John Mee

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Any tips for improving efficiency in general?

4 Answers4