I am trying to check whether the string starts and ends with the same word. eg earth
.
s=raw_input();
m=re.search(r"^(earth).*(earth)$",s)
if m is not None:
print "found"
my problem is when the string consists only of one word eg: earth
At present I have hard coded this case by
if m is not None or s=='earth':
print "found"
Is there any other way to do this?
EDIT:
words in a string are separated by spaces. looking for a regex solution
some examples
:
"earth is earth" ,"earth", --> valid
"earthearth", "eartheeearth", "earth earth mars" --> invalid
Use the str.startswith
and str.endswith
methods instead.
>>> 'earth'.startswith('earth')
True
>>> 'earth'.endswith('earth')
True
You can simply combine them into a single function:
def startsandendswith(main_str):
return main_str.startswith(check_str) and main_str.endswith(check_str)
And now we can call it:
>>> startsandendswith('earth', 'earth')
True
If, however, if the code matches words and not part of a word, it might be simpler to split the string, and then check if the first and last word are the string you want to check for:
def startsandendswith(main_str, check_str):
if not main_str: # guard against empty strings
return False
words = main_str.split(' ') # use main_str.split() to split on any whitespace
return words[0] == words[-1] == check_str
Running it:
>>> startsandendswith('earth', 'earth')
True
>>> startsandendswith('earth is earth', 'earth')
True
>>> startsandendswith('earthis earth', 'earth')
False
You can use backreference within regex
^(\w+\b)(.*\b\1$|$)
This would match a string only if it
You can use str.startswith
and str.endswith
:
>>> strs = "earthfooearth"
>>> strs.startswith('earth') and strs.endswith("earth")
True
>>> strs = "earth"
>>> strs.startswith('earth') and strs.endswith("earth")
True
Update:
If the words are separated by spaces and the start and end string is not known then use str.split
and str.rsplit
:
>>> strs = "foo bar foo"
>>> strs.split(None, 1)[0] == strs.rsplit(None, 1)[-1]
True
# single word
>>> strs = "foo"
>>> strs.split(None, 1)[0] == strs.rsplit(None, 1)[-1]
True
>>> strs = "foo bar ffoo"
>>> strs.split(None, 1)[0] == strs.rsplit(None, 1)[-1]
False
Here:
X = words.split()
X[:1] == X[-1:]
The slicing makes it work for empty strings too, and extend nicely to any number of words. If words
cannot be empty, use
X[0] == X[-1]
Well, if you absolutely want regex, you can make use of lookarounds, since they don't consume characters.
>>>import re
>>>s1 = 'earth is earth'
>>>s2 = 'earth'
>>>m = re.search(r"^(?=(earth)).*(earth)$",s1)
>>>m.group(1)
'earth'
>>>m.group(2)
'earth'
>>>m = re.search(r"^(?=(earth)).*(earth)$",s2)
>>>m.group(1)
'earth'
>>>m.group(2)
'earth'
For any string, you could perhaps use this:
^(?=([A-Za-z]+)).*(\1)$
I'm assuming words as being only alphabet characters. If you mean words as in non-space characters, then you may go for \\S
instead of [A-Za-z]
.
EDIT: Okay, it seems there's more to it. What I think might suit is:
^(?=(earth\b)).*((?:^|\s)\1)$
For the work earth. For any word stored in a variable named word
;
>>> word = 'earth' # Makes it so you can change it anytime
>>> pattern = re.compile('^(?=(' + word + '\b)).*((?:^|\s)\1)$')
>>> m.search(pattern, s)
Accepts:
earth is earth
earth
Rejects:
earthearth
eartheearth
earthis earth
And after that extract the captured groups or check whether the group are empty or not.
The bit I added is (?:^|\\s)
which checks for whether the word you're looking for is the only one in the 'sentence' or whether the word is in a sentence.
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