如何在字符串中的其他某些字符之后替换某些字符，Python？

Question

I have a string that is holding a URL:

url = http://example.com/1234/hello/

I wish to replace "hello" with "goodbye"

Thank you in advance!

Best Regards

Edit: My apologies, the example I used had a lot of placeholders. For extra clarification, "1234" and "hello" are dynamic and change a lot, so I need a method to replace everything after the 4th "/", if you will.

So far I've tried this, but it deleted the slashes and numbers:

url = re.search(r'(\A.*)0/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)1/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)2/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)3/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)4/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)5/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)6/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)7/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)8/',url,re.DOTALL|re.IGNORECASE).group(1)
url = re.search(r'(\A.*)9/',url,re.DOTALL|re.IGNORECASE).group(1)

Answer 1

You can use .split() and .join() :

split_url = url.split("/")
split_url[4] = "goodbye"
url = "/".join(split_url)

Answer 2

Are you looking for this (python 2.7)?

>>> import re
>>> input = ' http://example.com/1234/hello/'
>>> re.sub('((?:.*?/){4})([^/]+)(/?)', r'\1goodby\3', input)
' http://example.com/1234/goodby/'