Say I have a the string AAAGCTTACGAAAAAAACGTA and I would like to remove anything after and including the occurrence of 4 As, regardless of where it occurs in the string. So for this example we are left with AAAGCTTACG after trimming. What would be a fast and efficient way to go about this?
You can use str.split():
>>> s = "AAAGCTTACGAAAAAAACGTA"
>>> s.split("AAAA", 1)[0]
'AAAGCTTACG'
You could use a greedy match and replace with nothing.
import re
new_string = re.sub(r'AAAA.*', '', original_string)
Alternatively, AAAA can also be expressed as A{4} if you find it more readable.
Just find those AAAA if any, and slice:
>>> s = "AAAGCTTACGAAAAAAACGTA"
>>> s[:s.find("AAAA")]
'AAAGCTTACG'
However, this way you should first check whether the string contains AAAA, otherwise it will slice away the last character.
Related
While matching an email address, after I match something like yasar#webmail, I want to capture one or more of (\.\w+)(what I am doing is a little bit more complicated, this is just an example), I tried adding (.\w+)+ , but it only captures last match. For example, yasar#webmail.something.edu.tr matches but only include .tr after yasar#webmail part, so I lost .something and .edu groups. Can I do this in Python regular expressions, or would you suggest matching everything at first, and split the subpatterns later?
re module doesn't support repeated captures (regex supports it):
>>> m = regex.match(r'([.\w]+)#((\w+)(\.\w+)+)', 'yasar#webmail.something.edu.tr')
>>> m.groups()
('yasar', 'webmail.something.edu.tr', 'webmail', '.tr')
>>> m.captures(4)
['.something', '.edu', '.tr']
In your case I'd go with splitting the repeated subpatterns later. It leads to a simple and readable code e.g., see the code in #Li-aung Yip's answer.
You can fix the problem of (\.\w+)+ only capturing the last match by doing this instead: ((?:\.\w+)+)
This will work:
>>> regexp = r"[\w\.]+#(\w+)(\.\w+)?(\.\w+)?(\.\w+)?(\.\w+)?(\.\w+)?"
>>> email_address = "william.adama#galactica.caprica.fleet.mil"
>>> m = re.match(regexp, email_address)
>>> m.groups()
('galactica', '.caprica', '.fleet', '.mil', None, None)
But it's limited to a maximum of six subgroups. A better way to do this would be:
>>> m = re.match(r"[\w\.]+#(.+)", email_address)
>>> m.groups()
('galactica.caprica.fleet.mil',)
>>> m.group(1).split('.')
['galactica', 'caprica', 'fleet', 'mil']
Note that regexps are fine so long as the email addresses are simple - but there are all kinds of things that this will break for. See this question for a detailed treatment of email address regexes.
This is what you are looking for:
>>> import re
>>> s="yasar#webmail.something.edu.tr"
>>> r=re.compile("\.\w+")
>>> m=r.findall(s)
>>> m
['.something', '.edu', '.tr']
I'm the worst for regex in general, but in python... I need help in fixing my regex for parsing filenames, e.g:
>>> from re import search, I, M
>>> x="/almac/data/vectors_puces_T12_C1_00_d2v_H50_corr_m10_70.mtx"
>>> for i in range(6):
... print search(r"[vectors|pairs]+_(\w+[\-\w+]*[0-9]{0,4})([_T[0-9]{2,3}_C[1-9]_[0-9]{2}]?)(_[d2v|w2v|coocc\w*|doc\w*]*)(_H[0-9]{1,4})(_[sub|co[nvs{0,2}|rr|nc]+]?)(_m[0-9]{1,3}[_[0-9]{0,3}]?)",x, M|I).group(i)
...
It gives the following output:
vectors_puces_T12_C1_00_d2v_H50_corr_m10_70
puces_T
12_C1_00
_d2v
_H50
_corr
However, what I need is
vectors_puces_T12_C1_00_d2v_H50_corr_m10_70
puces
T12_C1_00
_d2v
_H50
_corr
I don't know what exactly is wrong. Thank you
One problem is that \w would also match underscore which you want to be a delimiter between puces and T12_C1_00 in this case. Replace the \w with A-Za-z\-. Also, you should put the underscore between the appropriate saving groups:
(?:vectors|pairs)_([A-Za-z\-]+[0-9]{0,4})_([T[0-9]{2,3}_C[1-9]_[0-9]{2}]?)...
HERE^
Works for me:
>>> import re
>>> re.search(r"(?:vectors|pairs)_([A-Za-z\-]+[0-9]{0,4})_([T[0-9]{2,3}_C[1-9]_[0-9]{2}]?)(_[d2v|w2v|coocc\w*|doc\w*]*)(_H[0-9]{1,4})(_[sub|co[nvs{0,2}|rr|nc]+]?)(_m[0-9]{1,3}[_[0-9]{0,3}]?)",x, re.M|re.I).groups()
('puces', 'T12_C1_00', '_d2v', '_H50', '_corr', '_m10_70')
I've also replaced the [vectors|pairs] with (?:vectors|pairs) which is, I think, what you've actually meant - match either vectors or pairs literal strings, (?:...) is a syntax for a non-capturing group.
I'm not sure what your goal is, but you seem to be interested in what's between each underscore, so it may be simpler to split by it:
path, filename = os.path.split(x)
filename = filename.split('.')
fileparts = filename.split('_')
fileparts will then be this list:
vectors
puces
T12
C1
00
d2v
H50
corr
m10
70
And you can validate / inspect any part, e.g. if fileparts[0] == 'vectors' or tpart = fileparts[2:4]...
I need a regular expression that accepts only characters having accents. For the moment I'm using this one:
[ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöœøùúûüýþÿ]*$
Is there another expression, which is clearer than my expression?
i think this will solve your problem :
[œÀ-ÖØ-öø-ÿ]*$
Since all characters except the œ are between characters 192 À and 255 ÿ, could you do something like looking ahead and checking they don't contain any of the characters in the range that you don't want? I'm not sure it improves anything compared to yours but it's a bit shorter and maybe, just maybe, clearer.
(?![÷×])[À-ÿœ]
Regex isn't always the clearest way to handle text, even if it is the fastest.
You could assign your regular expression to a variable, then insert it via text interpolation:
accent_chars = '[ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöœøùúûüýþÿ]'
my_regex = '^...%s*...$' % accent_chars
You can also use these ranges:
[œÀ-ÖØ-öø-ÿ]
Demonstration using Python 3:
>>> import re
>>> s = 'ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöœøùúûüýþÿ'
>>> ''.join(re.findall('[œÀ-ÖØ-öø-ÿ]', s))
'ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõöœøùúûüýþÿ'
>>> len(''.join(re.findall('[œÀ-ÖØ-öø-ÿ]', s))) == len(s)
True
The downside is that it is not immediately clear to someone unfamiliar with Unicode that this covers every desired case.
You could also try using the POSIX bracket expression [:alpha:].
Then just prune the alphabetic characters from your string.
I'd like your opinion as you might be more experienced on Python as I do.
I came from C++ and I'm still not used to the Pythonic way to do things.
I want to loop under a string, between 2 capital letters. For example, I could do that this way:
i = 0
str = "PythonIsFun"
for i, z in enumerate(str):
if(z.isupper()):
small = ''
x = i + 1
while(not str[x].isupper()):
small += str[x]
I wrote this on my phone, so I don't know if this even works but you caught the idea, I presume.
I need you to help me get the best results on this, not just in a non-forced way to the cpu but clean code too. Thank you very much
This is one of those times when regexes are the best bet.
(And don't call a string str, by the way: it shadows the built-in function.)
s = 'PythonIsFun'
result = re.search('[A-Z]([a-z]+)[A-Z]', s)
if result is not None:
print result.groups()[0]
you could use regular expressions:
import re
re.findall ( r'[A-Z]([^A-Z]+)[A-Z]', txt )
outputs ['ython'], and
re.findall ( r'(?=[A-Z]([^A-Z]+)[A-Z])', txt )
outputs ['ython', 's']; and if you just need the first match,
re.search ( r'[A-Z]([^A-Z]+)[A-Z]', txt ).group( 1 )
You can use a list comprehension to do this easily.
>>> s = "PythonIsFun"
>>> u = [i for i,x in enumerate(s) if x.isupper()]
>>> s[u[0]+1:u[1]]
'ython'
If you can't guarantee that there are two upper case characters you can check the length of u to make sure it is at least 2. This does iterate over the entire string, which could be a problem if the two upper case characters occur at the start of a lengthy string.
There are many ways to tackle this, but I'd use regular expressions.
This example will take "PythonIsFun" and return "ythonsun"
import re
text = "PythonIsFun"
pattern = re.compile(r'[a-z]') #look for all lower-case characters
matches = re.findall(pattern, text) #returns a list of lower-chase characters
lower_string = ''.join(matches) #turns the list into a string
print lower_string
outputs:
ythonsun
I want to use a regular expression that would do the following thing ( i extracted the part where i'm in trouble in order to simplify ):
any character for 1 to 5 first characters, then an "underscore", then some digits, then an "underscore", then some digits or dot.
With a restriction on "underscore" it should give something like that:
^([^_]{1,5})_([\\d]{2,3})_([\\d\\.]*)$
But i want to allow the "_" in the 1-5 first characters in case it still match the end of the regular expression, for example if i had somethink like:
to_to_123_12.56
I think this is linked to an eager problem in the regex engine, nevertheless, i tried to do some lazy stuff like explained here but without sucess.
Any idea ?
I used the following regex and it appeared to work fine for your task. I've simply replaced your initial [^_] with ..
^.{1,5}_\d{2,3}_[\d\.]*$
It's probably best to replace your final * with + too, unless you allow nothing after the final '_'. And note your final part allows multiple '.' (I don't know if that's what you want or not).
For the record, here's a quick Python script I used to verify the regex:
import re
strs = [ "a_12_1",
"abc_12_134",
"abcd_123_1.",
"abcde_12_1",
"a_123_123.456.7890.",
"a_12_1",
"ab_de_12_1",
]
myre = r"^.{1,5}_\d{2,3}_[\d\.]+$"
for str in strs:
m = re.match(myre, str)
if m:
print "Yes:",
if m.group(0) == str:
print "ALL",
else:
print "No:",
print str
Output is:
Yes: ALL a_12_1
Yes: ALL abc_12_134
Yes: ALL abcd_134_1.
Yes: ALL abcde_12_1
Yes: ALL a_123_123.456.7890.
Yes: ALL a_12_1
Yes: ALL ab_de_12_1
^(.{1,5})_(\d{2,3})_([\d.]*)$
works for your example. The result doesn't change whether you use a lazy quantifier or not.
While answering the comment ( writing the lazy expression ), i saw that i did a mistake... if i simply use the folowing classical regex, it works:
^(.{1,5})_([\\d]{2,3})_([\\d\\.]*)$
Thank you.