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How can I create an array of Unicode characters in Python?

I am using Repl.it.
import array as arr
my_array = arr.array("u", [u"3", u"6", u"9", u"12"])
print(my_array)
print(type(my_array))
print(type(my_array[0]))
The above source code produces the following error:
Traceback (most recent call last):
File "main.py", line 3, in <module>
my_array = arr.array("u", [u"3", u"6", u"9", u"12"])
TypeError: array item must be unicode character
Why the source code isn't working?

Array type "u" corresponds to a single Unicode character. The initializer contains a two-character item u"12". Perhaps you want something like:
arr.array("u", [u"3", u"6", u"9", u"1", u"2"])

Binascii.unhexlify typeerror Odd length string

I have written following script to get rid of non-alphanumeric characters, and get them back afterwards. However I can't seem to figure out why the unhexlify will not work. Any suggestions?
import binascii, timeit, re
damn_string = "asjke5234nlkfs$sfj3.$sfjk."
def convert_string(s):
return ''.join('__UTF%s__' % binascii.hexlify(c.encode('utf-16')) if not c.isalnum() else c for c in s.lower())
def convert_back(s):
for i in re.findall('__UTF([a-f0-9]{8})__', s): # For testing
print binascii.unhexlify(i).decode('utf-16')
return re.sub('__UTF([a-f0-9]{8})__', binascii.unhexlify('\g<1>').decode('utf-16'), s)
convert = convert_string(damn_string)
print convert
print convert_back(convert)
result in the following output:
asjke5234nlkfs__UTFfffe2400__sfj3__UTFfffe2e00____UTFfffe2400__sfjk__UTFfffe2e00__
$
.
$
.
Traceback (most recent call last):
File "test.py", line 131, in <module>
print convert_back(convert)
File "test.py", line 127, in convert_back
return re.sub('__UTF([a-f0-9]{8})__', binascii.unhexlify('\g<1>').decode('utf-16'), s)
TypeError: Odd-length string

My bad. I took me a bit too long to realize that re.sub cannot submit the group string in this manner. One way of doing this is:
return re.sub('__UTF([a-f0-9]{8})__', lambda x: binascii.unhexlify(x.group(1)).decode('utf-16'), s)

How to use variable in python regex?

I am trying to process user input in regex from variable. After a lot of searching I have come up with following:
Explaination of code variables:
step is a string used as input for regex
e.g.
replace|-|space ,
replace|*|null,
replace|/|\|squot|space
b is a list of elements. Element is fetched and modified as per regex.
i is integer received from other function to access list b using i as index
I process the above string to get array, then use the last element of array as substitution string
First element is deleted as it is not required.
All other elements need to be replaced with substitution string.
def replacer(step,i,b):
steparray = step.split('|')
del steparray[0]
final = steparray.pop()
if final == "space":
subst = u" "
elif final == "squot":
subst = u"'"
elif final == "dquot":
subst = u"\""
else:
subst = u"%s"%final
for input in xrange(0,len(steparray)):
test=steparray[input]
regex = re.compile(ur'%s'%test)
b[i] = re.sub(regex, subst, b[i])
print b[i]
However, when I run above code, following error is shown:
File "CSV_process.py", line 78, in processor
replacer(step,i,b)
File "CSV_process.py", line 115, in replacer
regex = re.compile(ur'%s'%test)
File "/usr/lib/python2.7/re.py", line 190, in compile
return _compile(pattern, flags)
File "/usr/lib/python2.7/re.py", line 242, in _compile
raise error, v # invalid expression
sre_constants.error: nothing to repeat
I tried a lot but dont understand how regex works. Please help with error.
Final requirement is to get a special character from user input and replace it with another character (again from user input)
PS: Also, the code does not have 242 lines but error is on line 242. Is the error occurring after end of array in for loop?

Some special characters like * should be escaped to match literally.
>>> import re
>>> re.compile('*')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "C:\Python27\lib\re.py", line 194, in compile
return _compile(pattern, flags)
File "C:\Python27\lib\re.py", line 251, in _compile
raise error, v # invalid expression
sre_constants.error: nothing to repeat
Using re.escape, you can escape them:
>>> print(re.escape('*'))
\*
>>> re.compile(re.escape('*'))
<_sre.SRE_Pattern object at 0x000000000273DF10>
BTW, if you want to simply replace them, regular expression is not necessary. Why don't you use str.replace?
replaced_string = string_object.replace(old, new)

python convert string "0" to float gives error

i have the following code in my python script, to launch an application and grab the output of it.
An example of this output would be 'confirmed : 0'
Now i only want to know the number, in this case zero, but normally this number is float, like 0.005464
When i run this code it tells me it cannot convert "0" to float. What am i doing wrong?
This is the error i get now:
ValueError: could not convert string to float: "0"
cmd = subprocess.Popen('/Applications/Electrum.app/Contents/MacOS/Electrum getbalance', shell=True, stdout=subprocess.PIPE)
for line in cmd.stdout:
if "confirmed" in line:
a,b=line.split(': ',1)
if float(b)>0:
print "Positive amount"
else:
print "Empty"

According to the exception you got, the value contained in b is not 0, but "0" (including the quotes), and therefore cannot be converted to a float directly. You'll need to remove the quotes first, e.g. with float(b.strip('"')).
As can be seen in the following examples, the exception description does not add the quotes, so they must have been part of the original string:
>>> float('"0"')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: "0"
>>> float('a')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
ValueError: could not convert string to float: a

I have tested the code and found that split(': ', 1) result contains string
>>> line = "1: 456: confirmed"
>>> "confirmed" in line
True
>>> a,b=line.split(': ', 1)
>>> a
'1'
>>> b
'456: confirmed'

Shorthand for defining PyParsing field names

I have a few pyparsing tokens defined as follows:
field = Word(alphas + "_").setName("field")
Is there really no shorthand for this?
Furthermore, this does not seem to work, the dictionary returned by expression.parseString() is always an empty one.

You are confusing setName and setResultsName. setName assigns a name to the expression so that exception messages are more meaningful. Compare:
>>> integer1 = Word(nums)
>>> integer1.parseString('x')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "c:\python26\lib\site-packages\pyparsing-1.5.6-py2.6.egg\pyparsing.py", line 1032, in parseString
raise exc
pyparsing.ParseException: Expected W:(0123...) (at char 0), (line:1, col:1)
and:
>>> integer2 = Word(nums).setName("integer")
>>> integer2.parseString('x')
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "c:\python26\lib\site-packages\pyparsing-1.5.6-py2.6.egg\pyparsing.py", line 1032, in parseString
raise exc
pyparsing.ParseException: Expected integer (at char 0), (line:1, col:1)
setName gives a name to the expression itself.
setResultsName on the other hand gives a name to the parsed data that is returned, like named fields in a regex.
>>> expr = integer.setResultsName('age') + integer.setResultsName('credits')
>>> data = expr.parseString('20 110')
>>> print data.dump()
['20', '110']
- age: 20
- credits: 110
And as #Kimvais has mentioned, there is a shortcut for setResultsName:
>>> expr = integer('age') + integer('credits')
Note also that setResultsName returns a copy of the expression - that is the only way that using the same expression multiple times with different names works.

field = Word(alphas + "_")("field")
seems to work.