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Replace Unicode code point with actual character using regex

I have a large file where any unicode character that wasn't in UTF-8 got replaced by its code point in angle brackets (e.g. the "👍" was converted to "<U+0001F44D>"). Now I want to revert this with a regex substitution.
I've tried to acomplish this with
re.sub(r'<U\+([A-F0-9]+)>',r'\U\1', str)
but obviously this won't work because we cannot insert the group into this unicode escape.
What's the best/easiest way to do this? I found many questions trying to do the exact opposite but nothing useful to 're-encode' these code points as actual characters...

When you have a number of the character, you can do ord(number) to get the character of that number.
Because we have a string, we need to read it as int with base 16.
Both of those together:
>>> chr(int("0001F44D", 16))
'👍'
However, now we have a small function, not a string to simply replace! Quick search returned that you can pass a function to re.sub
Now we get:
re.sub(r'<U\+([A-F0-9]+)>', lambda x: chr(int(x.group(1), 16)), my_str)
PS Don't name your string just str - you'll shadow the builtin str meaning type.

Changing string with escaped Unicode to normal Unicode

I've got a string which looks like this, made up of normal characters and one single escaped Unicode character in the middle:
reb\u016bke
I want to have Python convert the whole string to the normal Unicode version, which should be rebūke. I've tried using str.encode(), but it doesn't seem to do very much, and apparently decode doesn't exist anymore? I'm really stuck!
EDIT: Output from repr is reb\\\u016bke

If I try reproducing your issue:
s="reb\\u016bke";
print(s);
# reb\u016bke
print(repr(s));
# 'reb\\u016bke'
print(s.encode().decode('unicode-escape'));
# rebūke

Python re.sub() and unicode

I have what feels to me like a really basic question, but for the life of me I can't figure it out.
I have a whole bunch of text I'm going through and converting to the International Phonetic Alphabet. I'm using the re.sub() method a lot, and in many cases this means replacing a character of string type with a character of unicode type. For example:
for row in responsesIPA:
re.sub("3", u"\u0259", row)
I'm getting TypeError: expected string or buffer. The docs on Python re say that the type for the replacement has to match the type for what you're searching, so maybe that's the problem? I tried putting str() around u"\u0259", but I'm still getting the type error. Is there a way for me to do this replacement?

The error you're getting is telling you that the "row" isn't a valid string or buffer(str, bytes, unicode, anything that is readable), you will need to double check what is stored in row by adding a print(row) in front.
Just to prove that this is the case, doing so will work:
import re
print(re.sub("3", u"\u0259", "12345"))

Convert Unicode string to UTF-8, and then to JSON

I want to encode a string in UTF-8 and view the corresponding UTF-8 bytes individually. In the Python REPL the following seems to work fine:
>>> unicode('©', 'utf-8').encode('utf-8')
'\xc2\xa9'
Note that I’m using U+00A9 COPYRIGHT SIGN as an example here. The '\xC2\xA9' looks close to what I want — a string consisting of two separate code points: U+00C2 and U+00A9. (When UTF-8-decoded, it gives back the original string, '\xA9'.)
Then, I want the UTF-8-encoded string to be converted to a JSON-compatible string. However, the following doesn’t seem to do what I want:
>>> import json; json.dumps('\xc2\xa9')
'"\\u00a9"'
Note that it generates a string containing U+00A9 (the original symbol). Instead, I need the UTF-8-encoded string, which would look like "\u00C2\u00A9" in valid JSON.
TL;DR How can I turn '©' into "\u00C2\u00A9" in Python? I feel like I’m missing something obvious — is there no built-in way to do this?

If you really want "\u00c2\u00a9" as the output, give json a Unicode string as input.
>>> print json.dumps(u'\xc2\xa9')
"\u00c2\u00a9"
You can generate this Unicode string from the raw bytes:
s = unicode('©', 'utf-8').encode('utf-8')
s2 = u''.join(unichr(ord(c)) for c in s)
I think what you really want is "\xc2\xa9" as the output, but I'm not sure how to generate that yet.

Python: Convert Unicode-Hex-String to Unicode

I have a hex-string made from a unicode string with that function:
def toHex(s):
res = ""
for c in s:
res += "%02X" % ord(c) #at least 2 hex digits, can be more
return res
hex_str = toHex(u"...")
This returns a string like this one:
"80547CFB4EBA5DF15B585728"
That's a sequence of 6 chinese symbols.
But
u"Knödel"
converts to
"4B6EF664656C"
What I need now is a function to convert this back to the original unicode. The chinese symbols seem to have a 2-byte representation while the second example has 1-byte representations for all characters. So I can't just use unichr() for each 1- or 2-byte block.
I've already tried
binascii.unhexlify(hex_str)
but this seems to convert byte-by-byte and returns a string, not unicode. I've also tried
binascii.unhexlify(hex_str).decode(...)
with different formats. Never got the original unicode string.
Thank you a lot in advance!

This seems to work just fine:
binascii.unhexlify(binascii.hexlify(u"Knödel".encode('utf-8'))).decode('utf-8')
Comes back to the original object. You can do the same for the chinese text if it's encoded properly, however ord(x) already destroys the text you started from. You'll need to encode it first and only then treat like a string of bytes.

Can't be done. Using %02X loses too much information. You should be using something like UTF-8 first and converting that, instead of inventing a broken encoding.
>>> u"Knödel".encode('utf-8').encode('hex')
'4b6ec3b664656c'

When I was working with Unicode in a VB app a while ago the first 1 or 2 digits would be removed if they were a "0". Meaning "&H00A2" would automatically be converted to "&HA2", I just created a small function to check the length of the string and if it was less than 4 chars add the missing 0's. I'm not sure if this is what's happening to you, but I thought I would give bit of information as something to be aware of.