This question already has answers here:
'NoneType' object has no attribute 'group'
(4 answers)
Closed 3 years ago.
Regex search fails to get a string from match object when being used in a for loop.
row_values = result_script_name.split('^')
for row in row_values:
table_name = re.search(r"(?<=')(.*)(?=')", row).group(0)
AttributeError: 'NoneType' object has no attribute 'group'
But the same regex pattern finds string perfectly fine when used outside the loop.
table_name = re.search(r"(?<=')(.*)(?=')", row_values[0]).group(0)
The string I wanted was to get "lifetime" outof below string
^WORKFLOW_NAME='lifetime'
I believe what is happening is that certain rows do not match at all, and therefore you are trying to access a capture group (the zeroth one, in this case), which does not even exist. Here is the pattern you should be using:
input = "^WORKFLOW_NAME='lifetime'"
match = re.search(r"(?<=')(.*)(?=')", input)
if match:
print(match.group(0))
That is, you should first be checking if the call to search were successful, and only then print. I don't know exactly what your loop is supposed to be doing, but you can easily enough adapt the above script to your needs.
Here, we might want to simplify our expression, maybe to something similar to:
.+?'(.+?)'
where our data is saved in the capturing group \\1
Test
# coding=utf8
# the above tag defines encoding for this document and is for Python 2.x compatibility
import re
regex = r".+'(.+?)'"
test_str = "^WORKFLOW_NAME='lifetime'"
subst = "\\1"
# You can manually specify the number of replacements by changing the 4th argument
result = re.sub(regex, subst, test_str, 0, re.MULTILINE)
if result:
print (result)
# Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.
DEMO
RegEx
If this expression wasn't desired, it can be modified or changed in regex101.com.
RegEx Circuit
jex.im visualizes regular expressions:
Demo
const regex = /.+?'(.+?)'/gm;
const str = `^WORKFLOW_NAME='lifetime'
WORKFLOW_NAME='Any other data that we want'
WORKFLOW_NAME='Any other data that we want'`;
const subst = `$1`;
// The substituted value will be contained in the result variable
const result = str.replace(regex, subst);
console.log('Substitution result: ', result);
Related
I do not consider myself a newbie in regex, but I seem to have found a problem that stumped me (it's also Friday evening, so brain not at peak performance).
I am trying to substitute a place-holder inside a string with some other value. I am having great difficulty getting a syntax that behaves the way I want.
My place-holder has this format: {swap}
I want it to capture and replace these:
{swap} # NewValue
x{swap}x # xNewValuex
{swap}x # NewValuex
x{swap} # xNewValue
But I want it to NOT match these:
{{swap}} # NOT {NewValue}
x{{swap}}x # NOT x{NewValue}x
{{swap}}x # NOT {NewValue}x
x{{swap}} # NOT x{NewValue}
In all of the above, x can be any string, of any length, be it "word" or not.
I'm trying to do this using python3's re.sub() but anytime I satisfy one subset of criteria I lose another in the process. I'm starting to think it might not be possible to do in a single command.
Cheers!
If you're able to use the newer regex module, you can use (*SKIP)(*FAIL):
{{.*?}}(*SKIP)(*FAIL)|{.*?}
See a demo on regex101.com.
Broken down, this says:
{{.*?}}(*SKIP)(*FAIL) # match any {{...}} and "throw them away"
| # or ...
{.*?} # match your desired pattern
In Python this would be:
import regex as re
rx = re.compile(r'{{.*?}}(*SKIP)(*FAIL)|{.*?}')
string = """
{swap}
x{swap}x
{swap}x
x{swap}
{{swap}}
x{{swap}}x
{{swap}}x
x{{swap}}"""
string = rx.sub('NewValue', string)
print(string)
This yields:
NewValue
xNewValuex
NewValuex
xNewValue
{{swap}}
x{{swap}}x
{{swap}}x
x{{swap}}
For the sake of completeness, you can also achieve this with Python's own re module but here, you'll need a slightly adjusted pattern as well as a replacement function:
import re
rx = re.compile(r'{{.*?}}|({.*?})')
string = """
{swap}
x{swap}x
{swap}x
x{swap}
{{swap}}
x{{swap}}x
{{swap}}x
x{{swap}}"""
def repl(match):
if match.group(1) is not None:
return "NewValue"
else:
return match.group(0)
string = rx.sub(repl, string)
print(string)
Use negative lookahead and lookbehind:
s1 = "x{swap}x"
s2 = "x{{swap}}x"
pattern = r"(?<!\{)\{[^}]+\}(?!})"
re.sub(pattern, "foo", s1)
#'xfoox'
re.sub(pattern, "foo", s2)
#'x{{swap}}x'
I tried to search but the information that I am getting seems to be kinda overwhelming and far from what I need. I can't seem to get it to work.
The requirement is to get the function that starts with "meta" and its parentheses.
input:
one metaOmph(uno)
one metaAsdf(dos)
one metaPoil(tres)
output:
[ metaOmph , (uno) ]
[ metaAsdf, (dos) ]
[ metaPoil, (tres)]
The one that I currently have just gets the entire line if it starts with "meta". so I have the entire "one meta<>" if it's a match, would it be possible do what I'm aiming for?
Edit: It's one input/line at a time.
I'd love to post what I did earlier but I closed repl.it due to my frustration. I'll keep it in mind on my next post. (quite new here)
import re
s = """one metaOmph(uno)
one metaAsdf(dos)
one metaPoil(tres)"""
print(re.findall(".+(meta\w+)(\(\w+\))", s))
Outputs:
[('metaOmph', '(uno)'), ('metaAsdf', '(dos)'), ('metaPoil', '(tres)')]
re.findall() approach with valid regex pattern:
import re
s = '''
one metaOmph(uno)
one metaAsdf(dos)
one metaPoil(tres)
'''
result = re.findall(r'\b(meta\w+)(\([^()]+\))', s)
print(result)
The output:
[('metaOmph', '(uno)'), ('metaAsdf', '(dos)'), ('metaPoil', '(tres)')]
If you are going to pass a multiline string, it would seem simple to use the module level re.findall function.
text = '''one metaOmph(uno)
one metaAsdf(dos)
one metaPoil(tres)'''
r = re.findall(r'\b(meta.*?)(\(.*?\))', text, re.M)
print(r)
[('metaOmph', '(uno)'), ('metaAsdf', '(dos)'), ('metaPoil', '(tres)')]
If you are going to be passing 1-line strings as input to a loop, it might make more sense to compile the pattern beforehand, using re.compile and re.search inside a function:
pat = re.compile(r'\b(meta.*?)(\(.*?\))')
def find(text):
return pat.search(text)
for text in list_of_texts: # assuming you're passing in your strings from a list, or elsewhere
m = find(text)
if m:
print(list(m.groups()))
['metaOmph', '(uno)']
['metaAsdf', '(dos)']
['metaPoil', '(tres)']
Note that m might return a match object or None depending on whether a search was found. You'll want to query the return value, otherwise you'll receive an AttributeError: 'NoneType' object has no attribute 'groups', or something along those lines.
Alternatively, if you want to append the result to a list, you might instead use:
r_list = []
for text in list_of_texts:
m = find(text)
if m:
r_list.append(list(m.groups()))
print(r_list)
[['metaOmph', '(uno)'], ['metaAsdf', '(dos)'], ['metaPoil', '(tres)']]
Regex Details
\b # word boundary (thought to add this in thanks to Roman's answer)
(
meta # literal 'meta'
.*? # non-greedy matchall
)
(
\( # literal opening brace (escaped)
.*?
\) # literal closing brace (escaped)
)
>>> import re
>>> s = 'this is a test'
>>> reg1 = re.compile('test$')
>>> match1 = reg1.match(s)
>>> print match1
None
in Kiki that matches the test at the end of the s. What do I miss? (I tried re.compile(r'test$') as well)
Use
match1 = reg1.search(s)
instead. The match function only matches at the start of the string ... see the documentation here:
Python offers two different primitive operations based on regular expressions: re.match() checks for a match only at the beginning of the string, while re.search() checks for a match anywhere in the string (this is what Perl does by default).
Your regex does not match the full string. You can use search instead as Useless mentioned, or you can change your regex to match the full string:
'^this is a test$'
Or somewhat harder to read but somewhat less useless:
'^t[^t]*test$'
It depends on what you're trying to do.
It's because of that match method returns None if it couldn't find expected pattern, if it find the pattern it would return an object with type of _sre.SRE_match .
So, if you want Boolean (True or False) result from match you must check the result is None or not!
You could examine texts are matched or not somehow like this:
string_to_evaluate = "Your text that needs to be examined"
expected_pattern = "pattern"
if re.match(expected_pattern, string_to_evaluate) is not None:
print("The text is as you expected!")
else:
print("The text is not as you expected!")
This question already has answers here:
Why does re.sub replace the entire pattern, not just a capturing group within it?
(4 answers)
Closed 2 years ago.
I am very new to python
I need to match all cases by one regex expression and do a replacement. this is a sample substring --> desired result:
<cross_sell id="123" sell_type="456"> --> <cross_sell>
i am trying to do this in my code:
myString = re.sub(r'\<[A-Za-z0-9_]+(\s[A-Za-z0-9_="\s]+)', "", myString)
instead of replacing everything after <cross_sell, it replaces everything and just returns '>'
is there a way for re.sub to replace only the capturing group instead of the entire pattern?
You can use substitution groups:
>>> my_string = '<cross_sell id="123" sell_type="456"> --> <cross_sell>'
>>> re.sub(r'(\<[A-Za-z0-9_]+)(\s[A-Za-z0-9_="\s]+)', r"\1", my_string)
'<cross_sell> --> <cross_sell>'
Notice I put the first group (the one you want to keep) in parenthesis and then I kept that in the output by using the "\1" modifier (first group) in the replacement string.
You can use a group reference to match the first word and a negated character class to match the rest of the string between <> :
>>> s='<cross_sell id="123" sell_type="456">'
>>> re.sub(r'(\w+)[^>]+',r'\1',s)
'<cross_sell>'
\w is equal to [A-Za-z0-9_].
Since the input data is XML, you'd better parse it with an XML parser.
Built-in xml.etree.ElementTree is one option:
>>> import xml.etree.ElementTree as ET
>>> data = '<cross_sell id="123" sell_type="456"></cross_sell>'
>>> cross_sell = ET.fromstring(data)
>>> cross_sell.attrib = {}
>>> ET.tostring(cross_sell)
'<cross_sell />'
lxml.etree is an another option.
below code tested under python 3.6 , without use group..
test = '<cross_sell id="123" sell_type="456">'
resp = re.sub(r'\w+="\w+"' ,r'',test)
print (resp)
<cross_sell>
I wrote a script to catch and correct commands before they are read by a parser. The parser requires equal, not equal, greater, etc, entries to be separated by commas, such as:
'test(a>=b)' is wrong
'test(a,>=,b)' is correct
The script i wrote works fine, but i would love to know if there's a more efficient way to do this.
Here's my script:
# Correction routine
def corrector(exp):
def rep(exp,a,b):
foo = ''
while(True):
foo = exp.replace(a,b)
if foo == exp:
return exp
exp = foo
# Replace all instances with a unique identifier. Do it in a specific order
# so for example we catch an instance of '>=' before we get to '='
items = ['>=','<=','!=','==','>','<','=']
for i in range(len(items)):
exp = rep(exp,items[i],'###%s###'%i)
# Re-add items with commas
for i in range(len(items)):
exp = exp.replace('###%s###'%i,',%s,'%items[i])
# Remove accidental double commas we may have added
return exp.replace(',,',',')
print corrector('wrong_syntax(b>=c) correct_syntax(b,>=,c)')
// RESULT: wrong_syntax(b,>=,c) correct_syntax(b,>=,c)
thanks!
As mentioned in the comments, one approach would be to use a regular expression. The following regex matches any of your operators when they are not surrounded by commas, and replaces them with the same string with the commas inserted:
inputstring = 'wrong_syntax(b>=c) correct_syntax(b,>=,c)'
regex = r"([^,])(>=|<=|!=|==|>|<|=)([^,])"
replace = r"\1,\2,\3"
result = re.sub(regex, replace, inputstring)
print(result)
Simple regexes are relatively easy, but they can get complicated quickly. Check out the docs for more info:
http://docs.python.org/2/library/re.html
Here is a regex that will do what you asked:
import re
regex = re.compile(r'''
(?<!,) # Negative lookbehind
(!=|[><=]=?)
(?!,) # Negative lookahead
''', re.VERBOSE)
print regex.sub(r',\1,', 'wrong_expression(b>=c) or right_expression(b,>=,c)')
outputs
wrong_expression(b,>=,c) or right_expression(b,>=,c)