如何暂时忽略标点符号？ 蟒蛇

Question

hi i'm trying to write a function to decode a message the user entered

decypherbook = {'0000':8, '0001':1, '0010':0, '0011':9, '0100':5, '0101':3, '0110':7, '0111':2, '1110':4, '1111':6} 
userdecode = raw_input("Enter the number you want to de-cypher: ")
def decode(cypher, msg):
    length = len(msg)
    decoded = ""
    key_index = 0 ## starting position of a key in message
    while key_index < length: 
        key = msg[key_index:key_index + 4]
        decoded += str(cypher[key])
        key_index += 4
    return decoded

print "After de-cypher: ", decode(decypherbook, userdecode)

but if the user input a message like "0001,0001", which i would like the result be "1,1". How could i make my code temporarily ignore punctuation so it doesn't mess up with my indexing +4 in my code and still able to print out the punctuation later?

Answer 1

You can check if the next characeter is an integer. If not, just add it to the string and continue to the next character:

def decode(cypher, msg):
    length = len(msg)
    decoded = ""
    key_index = 0 ## starting position of a key in message
    while key_index < length: 
        key = msg[key_index:key_index + 4]
        decoded += str(cypher[key])
        key_index += 4

        # Pass every non digit after
        while key_index < length and not msg[key_index].isdigit():
             decoded += msg[key_index]
             key_index += 1

    return decoded

Here is an example of execution:

>>> def decode(cypher, msg):
... # ...
>>> decode(decypherbook, '0001,0010')
'1,0'

Side note: You could also prefer to make a list as a buffer instead of recreating a string every time (string are immutable, every += creates a new object) and do ''.join(buffer) at the end. Just for performance purpose.

Answer 2

Use split method from string object

userdecode = raw_input("Enter the number you want to de-cypher: ")
userdecode_list = userdecode.split(",")

And than call your function like this with join method from string object

print "After de-cypher: ", decode(decypherbook, "".join(userdecode_list))

Answer 3

I feel like replace matches your need more.

def decode(cypher, msg):
    for key, value in cypher.items():
        msg = msg.replace(key, str(value))

    return msg

Answer 4

A fun-one-liner (which assumes userdecode is guaranteed to be of the form r"(\\d{4},)*" )

def decode(cypher, msg):
    return ",".join([str(cypher[x]), for x in userdecode.split(",")])