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How to fix bad escape regex error (python re)

I've been messing around with re.sub() to see how I would change the format from Y-m-d to M/d/y. To perform the test, I defined the starting variable: current_date = "2012-05-26"
I would try to achieve to convert that date to 05/26/2012.
I tried to achieve this without using DateTime but with regex. I used re.sub as below:
formatted_date = re.sub(r"\d{2,4}-\d{1,2}-\d{1,2}", r"[^a-zA-Z]\d{1,2}/\d{1,2}/\d{2,4}", current_date)
The first regex is to match the original format of Y-M-D and the second Regex is to try to convert it to the format that I want it to be. I got the following error:
Traceback (most recent call last):
File "C:\Users\ghub4\AppData\Local\Programs\Python\Python39\lib\sre_parse.py", line 1039, in parse_template
this = chr(ESCAPES[this][1])
KeyError: '\\d'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "c:\Users\ghub4\OneDrive\Desktop\test_sub.py", line 5, in <module>
formatted_date = re.sub(r"\d{2,4}-\d{1,2}-\d{1,2}", r"[^a-zA-Z]\d{1,2}/\d{1,2}/\d{2,4}", current_date)
File "C:\Users\ghub4\AppData\Local\Programs\Python\Python39\lib\re.py", line 210, in sub
return _compile(pattern, flags).sub(repl, string, count)
File "C:\Users\ghub4\AppData\Local\Programs\Python\Python39\lib\re.py", line 327, in _subx
template = _compile_repl(template, pattern)
File "C:\Users\ghub4\AppData\Local\Programs\Python\Python39\lib\re.py", line 318, in _compile_repl
return sre_parse.parse_template(repl, pattern)
File "C:\Users\ghub4\AppData\Local\Programs\Python\Python39\lib\sre_parse.py", line 1042, in parse_template
raise s.error('bad escape %s' % this, len(this))
re.error: bad escape \d at position 9
Full Code:
import re
current_date = "2012-05-26"
formatted_date = re.sub(r"\d{2,4}-\d{1,2}-\d{1,2}", r"[^a-zA-Z]\d{1,2}/\d{1,2}/\d{2,4}", current_date)
print(formatted_date)
I've traced the error to potential the second regex but I'm unsure where position 9 is and how to fix the error. Another reason why I'm not sure how to fix it is due to the first error where it stated a keyerror raised by \\d. I'm sure that when the regex is interpret somewhere in the code, it is taking the \d as \\d instead which Im also not sure how to prevent that. I'm also pretty sure that the second regex may backfire on me and I am working on a solution on that after this question is posted. How would I be able to correct these errors?

The replacement string for a regex is not a regex in itself, rather it is a string which may contain references to groups captured by the original regex. In your case, you want to capture the year, month and day and then output them in the result string. You do that with () around the values you want to capture, and then refer to the groups by \1, \2, and \3 in the replacement string, with the numbers being assigned in order of the groups being captured. So for your code, you want:
formatted_date = re.sub(r"(\d{2,4})-(\d{1,2})-(\d{1,2})", r"\2/\3/\1", current_date)

Try and group your digits (If you goal is testing then position 9 is your first \d in your second regex-check - It is an invalid group reference):
formatted_date = re.sub(r"(\d{2,4})-(\d{1,2})-(\d{1,2})",r"\2/\3/\1",current_date)

What is the RegEx pattern for 24-06-2015 10:15:45: Aditya Krishnakant:?

What is the RegEx pattern for 24-06-2015 10:15:45: Aditya Krishnakant:
If you look at the whatsapp chat transcript, it looks like a mess. The purpose of this code is to print messages sent by a person in a new line (for better readability). This is my code
import re
f = open("wa_chat.txt", "r")
match = re.findall(r'(\d{2})\:(\d{2})\:(\d{4})\s(\d{2})\:(\d{2})\:(\d{2})\:\s(\w)\s(\w)\:', f)
for content in match:
print(f.readlines(), '\n')
f.close()
I am getting the following error message:
Traceback (most recent call last):
File "whatsapp.py", line 4, in <module>
match = re.findall(r'(\d{2})\:(\d{2})\:(\d{4})\s(\d{2})\:(\d{2})\:(\d{2})\:\s(\w)\s(\w)\:', f)
File "/usr/lib/python2.7/re.py", line 177, in findall
return_compile(pattern, flags).findall(string)
TypeError: expected string or buffer
Where am I going wrong?

For some reason you're putting \: where - should be. Also, instead of \s you can be more specific and just use a space. You can be more specific with those kinds of things because you know exactly what the format is. Your other big problem is that you're only using \w, which only matches one alphanumeric character, when you should use \w+, matching the whole word. Lastly, your actual error is coming from the fact that you're passing in a file object instead of the string containing its contents, i.e. f.read(). Here's some code that should work:
import re
f = open("wa_chat.txt", 'r')
match = re.findall(r'(\d{2})-(\d{2})-(\d{4}) (\d{2}):(\d{2}):(\d{2}): (\w+) (\w+):', f.read())
print match #or do whatever you want with it
Note that match will be a list of tuples since you wanted to use grouping.

Python regular expression NoneType error

I have a text file named "filename.txt"
content of file:
This is just a text
content to store
in a file.
i have made two python scripts to extract "to" from the text file
my 1st script:
#!/usr/bin/python
import re
f = open("filename.txt","r")
for line in f:
text = re.match(r"content (\S+) store",line)
x = text.group(1)
print x
my 2nd script:
#!/usr/bin/python
import re
f = open("filename.txt","r")
for line in f:
text = re.match(r"content (\S+) store",line)
if text:
x = text.group(1)
print x
2nd script gives the correct output
bash-3.2$ ./script2.py
to
but 1st script gives me an error
bash-3.2$ ./script1.py
Traceback (most recent call last):
File "./script1.py", line 6, in ?
x = text.group(1)
AttributeError: 'NoneType' object has no attribute 'group'
how is that adding an "if" condition gives me the correct output and when i remove it i get an error?

The error is pretty self-explanatory to me: re.match returns None if no match is found (see doc).
So when your regex doesn't match (eg first line), you're trying to access the group property of a NoneType object, it throws an error.
In the other case, you only access the property if text isn't None (since this is what the if text: checks, among other things).

This is because in your first code, your regex fails to match anything and therefore text is a NoneType. When you try to do group it throws the AttributeError: 'NoneType' object has no attribute 'group' error
However, for your regex, your code doesn't fail because you are careful to call group only if something was actually matched
Your second method is better since it's fail proof unlike the first one.

Python TypeError when using variable in re.sub

I'm new to python and I keep getting an error doing the simpliest thing.
I'm trying to use a variable in a regular expression and replace that with an *
the following gets me the error "TypeError: not all arguments converted during string formatting" and I can't tell why. this should be so simple.
import re
file = "my123filename.zip"
pattern = "123"
re.sub(r'%s', "*", file) % pattern
Error:
Traceback (most recent call last):
File "", line 1, in ?
TypeError: not all arguments converted during string formatting
Any tips?

You're problem is on this line:
re.sub(r'%s', "*", file) % pattern
What you're doing is replacing every occurance of %s with * in the text from the string file (in this case, I'd recommend renaming the variable filename to avoid shadowing the builtin file object and to make it more explicit what you're working with). Then you're trying to replace the %s in the (already replaced) text with pattern. However, file doesn't have any format modifiers in it which leads to the TypeError you see. It's basically the same as:
'this is a string' % ("foobar!")
which will give you the same error.
What you probably want is something more like:
re.sub(str(pattern),'*',file)
which is exactly equivalent to:
re.sub(r'%s' % pattern,'*',file)

Try re.sub(pattern, "*", file)? Or maybe skip re altogether and just do file.replace("123", "*").

Python re "bogus escape error"

I've been messing around with the python re modules .search method. cur is the input from a Tkinter entry widget. Whenever I enter a "\" into the entry widget, it throws this error. I'm not all to sure what the error is or how to deal with it. Any insight would be much appreciated.
cur is a string
tup[0] is also a string
Snippet:
se = re.search(cur, tup[0], flags=re.IGNORECASE)
The error:
Exception in Tkinter callback
Traceback (most recent call last):
File "C:\Python26\Lib\Tkinter.py", line 1410, in __call__
return self.func(*args)
File "C:\Python26\Suite\quidgets7.py", line 2874, in quick_links_results
self.quick_links_results_s()
File "C:\Python26\Suite\quidgets7.py", line 2893, in quick_links_results_s
se = re.search(cur, tup[0], flags=re.IGNORECASE)
File "C:\Python26\Lib\re.py", line 142, in search
return _compile(pattern, flags).search(string)
File "C:\Python26\Lib\re.py", line 245, in _compile
raise error, v # invalid expression
error: bogus escape (end of line)

"bogus escape (end of line)" means that your pattern ends with a backslash. This has nothing to do with Tkinter. You can duplicate the error pretty easily in an interactive shell:
>>> import re
>>> pattern="foobar\\"
>>> re.search(pattern, "foobar")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/re.py", line 142, in search
return _compile(pattern, flags).search(string)
File "/Library/Frameworks/Python.framework/Versions/2.5/lib/python2.5/re.py", line 241, in _compile
raise error, v # invalid expression
sre_constants.error: bogus escape (end of line)
The solution? Make sure your pattern doesn't end with a single backslash.

The solution to this issue is to use a raw string as the replacement text. The following won't work:
re.sub('this', 'This \\', 'this is a text')
It will throw the error: bogus escape (end of line)
But the following will work just fine:
re.sub('this', r'This \\', 'this is a text')
Now, the question is how do you convert a string generated during program runtime into a raw string in Python. You can find a solution for this here. But I prefer using a simpler method to do this:
def raw_string(s):
if isinstance(s, str):
s = s.encode('string-escape')
elif isinstance(s, unicode):
s = s.encode('unicode-escape')
return s
The above method can convert only ascii and unicode strings into raw strings. Well, this has been working great for me till date :)

If you are trying to search for "cur" in "tup[0]" you should do this through "try:... except:..." block to catch invalid pattern:
try :
se = re.search(cur, tup[0], flags=re.IGNORECASE)
except re.error, e:
# print to stdout or any status widget in your gui
print "Your search pattern is not valid."
# Some details for error:
print e
# Or some other code for default action.

The first parameter to re is the pattern to search for, thus if 'cur' contains a backslash at the end of the line, it'll be an invalid escape sequence. You've probably swapped your arguments around (I don't know what tup[0] is, but is it your pattern?) and it should be like this
se = re.search(tup[0], cur, flags=re.IGNORECASE)
As you very rarely use user input as a pattern (unless you're doing a regular expression search mechanism, in which case you might want to show the error instead).
HTH.
EDIT:
The error it is reporting is that you're using an escape character before the end of line (which is what bogus escape (end of line) means), that is your pattern ends with a backslash, which is not a valid pattern. Escape character (backslash) must be followed by another character, which removes or adds special meaning to that character (not sure exactly how python does it, posix makes groups by adding escape to parentheses, perl removes the group effect by escaping it). That is \* matches a literal asterix, whereas * matches the preceding character 0 or more times.