Develop Reference

How to check if a line contains a string in Python

I'm trying to check if a subString exists in a string using regular expression.
RE : re_string_literal = '^"[a-zA-Z0-9_ ]+"$'
The thing is, I don't want to match any substring. I'm reading data from a file:
Now one of the lines have this text:
cout<<"Hello"<<endl;
I just want to check if there's a string inside the line and if yes, store it in a list.
I have tried the re.match method but it only works if we have to match a pattern, but in this case, I just want to check if a string exists or not, if yes, store it somewhere.
re_string_lit = '^"[a-zA-Z0-9_ ]+"$'
text = 'cout<<"Hello World!"<<endl;'
re.match(re_string_lit,text)
It doesn't output anything.
In simple words,
I just want to extract everything inside ""

If you just want to extract everything inside "" then string splitting would be much simpler way of doing things.
>>> a = 'something<<"actualString">>something,else'
>>> b = a.split('"')[1]
>>> b
'actualString'
The above example would only work for not more than 2 instances of double quotes ("), but you could make it work by iterating over every substring extracted using split method and applying a much simpler Regular Expression.

This worked for me:
re.search('"(.+?)"', 'cout<<"Hello"<<endl')

python regular expression not matching file contents with re.match and re.MULTILINE flag

I'm reading in a file and storing its contents as a multiline string. Then I loop through some values I get from a django query to run regexes based on the query results values. My regex seems like it should be working, and works if I copy the values returned by the query, but for some reason isn't matching when all the parts are working together that ends like this
My code is:
with open("/path_to_my_file") as myfile:
data=myfile.read()
#read saved settings then write/overwrite them into the config
items = MyModel.objects.filter(some_id="s100009")
for item in items:
regexString = "^\s*"+item.feature_key+":"
print regexString #to verify its what I want it to be, ie debug
pq = re.compile(regexString, re.M)
if pq.match(data):
#do stuff
So basically my problem is that the regex isn't matching. When I copy the file contents into a big old string, and copy the value(s) printed by the print regexString line, it does match, so I'm thinking theres some esoteric python/django thing going on (or maybe not so esoteric as python isnt my first language).
And for examples sake, the output of print regexString is :
^\s*productDetailOn:
File contents:
productDetailOn:true,
allOff:false,
trendingWidgetOn:true,
trendingWallOn:true,
searchResultOn:false,
bannersOn:true,
homeWidgetOn:true,
}
Running Python 2.7. Also, dumped the types of both item.feature and data, and both were unicode. Not sure if that matters? Anyway, I'm starting to hit my head off the desk after working this for a couple hours, so any help is appreciated. Cheers!

According to documentation, re.match never allows searching at the beginning of a line:
Note that even in MULTILINE mode, re.match() will only match at the beginning of the string and not at the beginning of each line.
You need to use a re.search:
regexString = r"^\s*"+item.feature_key+":"
pq = re.compile(regexString, re.M)
if pq.search(data):
A small note on the raw string (r"^\s+"): in this case, it is equivalent to "\s+" because there is no \s escape sequence (like \r or \n), thus, Python treats it as a raw string literal. Still, it is safer to always declare regex patterns with raw string literals in Python (and with corresponding notations in other languages, too).

How can I identify invisible characters in python strings?

SHORT VERSION
I am retrieving a database value, which contains a short, but full HTML structure. I want to strip away all of the HTML-tags, and just end up with a single value. The HTML surrounding my relevant info, is always the same, and I just need to figure out what kind of line breaks, tabs or whitespaces the string contains, so that I can make a match, and remove it.
Is there a place I can paste the String online, or another way I can check the actual content of the String, so that I'll be able to remove it?
LONG VERSION, and what I've already tried:
The String is retrieved from a HP Quality Center database, and printed in the console of the automated test execution, the string is interpreted to show as two whitespaces. When pasted into word, eclipse or the QC script editor, it is shown as a linebreak.
I've tried to replace the whitespaces with \n, double whitespace and ¶. Nothing works.
I am translatnig this script from a working VBScript. The problematic invisible characters are defined as vbcrlf and VBCRLF there. For some reason they use lower case in the replace String before the relevant parameter value, and upper case in the string that comes after my relevant substring. They are defined as variables, and are not inside the String itself: <html>"&vbcrlf&"<body>"&vbcrlf&"<div...
This website suggests that I should use \n https://answers.yahoo.com/question/index?qid=20070506205148AAmr92N, as they write:
vbCrLf = "\n" # Carriage returnlinefeed combination
I am a little confused by the inconsitency of the upper/lower case use here though...
EDIT:
After googling Carriage returnlinefeed combination, i learned that it can be defined as /r/n here: Order of carriage return and new line feed.
But I spent an awful long time finding it, and it doesn't answer my question, of how I better can identify exactly what kind of invisible characters a string contains. I'll leave the question open.

To view the contents of a string (including it's "hidden" values) you can always do:
print( [data] )
# or
print( repr(data) )
If you're in a system which you described in the comments you can also do:
with open('/var/log/debug.log', 'w') as fh:
fh.write( str( [data] ) )
This will however just give you a general idea of what your data looks like, but if that solves your question or problem then that is great. If you need further assistance, edit your question or submit a new one :)

Python - replace multiline string in a file

I'm writing a script which finds in a file a few lines of text. I wonder how to replace exactly that text with other given (new string might be shorter or longer). I'm using re.compile() to create a multiple line pattern then looking for any match in a file I do like this:
for match in pattern.finditer(text_in_file)
#if it would be possible I wish to change
#text in a file here by (probably) replacing match.group(0)
Is it possible to accomplish in this way (if yes, then how to do it in the easiest way?) or my approach is wrong or hard to do it right (if yes, then how to do it right?)

The simple solution:
Read the whole text into a variable as a string.
Use a multi-line regexp to match what you want to replace
Use output = pattern.sub('replacement', fileContent)
The complex solution:
Read the file line by line
Print any line which doesn't match the start of the pattern
If you find a match for the start, stop printing until you see the end pattern.
If you saw the end pattern, print the replacement

Use pattern.sub('replacement text', text_in_file) to replace matches.
You can use back references in the replacement pattern as needed. It doesn't matter if the string is shorter or longer; the method returns a new string value with the replacements made. If the text came from a file, you'll need to write back the text to that file to replace the contents.
You could use the fileinput module if you need to make the replacement in-place; the module takes care of moving the original file aside and write a new file in it's place.

in python find index in list if combination of strings exist

I'm writing my first script and trying to learn python.
But I'm stuck and can't get out of this one.
I'm writing a script to change file names.
Lets say I have a string = "this.is.tEst3.E00.erfeh.ervwer.vwtrt.rvwrv"
I want the result to be string = "This Is Test3 E00"
this is what I have so far:
l = list(string)
//Transform the string into list
for i in l:
if "E" in l:
p = l.index("E")
if isinstance((p+1), int () is True:
if isinstance((p+2), int () is True:
delp = p+3
a = p-3
del l[delp:]
new = "".join(l)
new = new.replace("."," ")
print (new)
get in index where "E" and check if after "E" there are 2 integers.
Then delete everything after the second integer.
However this will not work if there is an "E" anyplace else.
at the moment the result I get is:
this is tEst
because it is finding index for the first "E" on the list and deleting everything after index+3
I guess my question is how do I get the index in the list if a combination of strings exists.
but I can't seem to find how.
thanks for everyone answers.
I was going in other direction but it is also not working.
if someone could see why it would be awesome. It is much better to learn by doing then just coping what others write :)
this is what I came up with:
for i in l:
if i=="E" and isinstance((i+1), int ) is True:
p = l.index(i)
print (p)
anyone can tell me why this isn't working. I get an error.
Thank you so much

Have you ever heard of a Regular Expression?
Check out python's re module. Link to the Docs.
Basically, you can define a "regex" that would match "E and then two integers" and give you the index of it.
After that, I'd just use python's "Slice Notation" to choose the piece of the string that you want to keep.
Then, check out the string methods for str.replace to swap the periods for spaces, and str.title to put them in Title Case

An easy way is to use a regex to find up until the E followed by 2 digits criteria, with s as your string:
import re
up_until = re.match('(.*?E\d{2})', s).group(1)
# this.is.tEst3.E00
Then, we replace the . with a space and then title case it:
output = up_until.replace('.', ' ').title()
# This Is Test3 E00

The technique to consider using is Regular Expressions. They allow you to search for a pattern of text in a string, rather than a specific character or substring. Regular Expressions have a bit of a tough learning curve, but are invaluable to learn and you can use them in many languages, not just in Python. Here is the Python resource for how Regular Expressions are implemented:
http://docs.python.org/2/library/re.html
The pattern you are looking to match in your case is an "E" followed by two digits. In Regular Expressions (usually shortened to "regex" or "regexp"), that pattern looks like this:
E\d\d # ('\d' is the specifier for any digit 0-9)
In Python, you create a string of the regex pattern you want to match, and pass that and your file name string into the search() method of the the re module. Regex patterns tend to use a lot of special characters, so it's common in Python to prepend the regex pattern string with 'r', which tells the Python interpreter not to interpret the special characters as escape characters. All of this together looks like this:
import re
filename = 'this.is.tEst3.E00.erfeh.ervwer.vwtrt.rvwrv'
match_object = re.search(r'E\d\d', filename)
if match_object:
# The '0' means we want the first match found
index_of_Exx = match_object.end(0)
truncated_filename = filename[:index_of_Exx]
# Now take care of any more processing
Regular expressions can get very detailed (and complex). In fact, you can probably accomplish your entire task of fully changing the file name using a single regex that's correctly put together. But since I don't know the full details about what sorts of weird file names might come into your program, I can't go any further than this. I will add one more piece of information: if the 'E' could possibly be lower-case, then you want to add a flag as a third argument to your pattern search which indicates case-insensitive matching. That flag is 're.I' and your search() method would look like this:
match_object = re.search(r'E\d\d', filename, re.I)
Read the documentation on Python's 're' module for more information, and you can find many great tutorials online, such as this one:
http://www.zytrax.com/tech/web/regex.htm
And before you know it you'll be a superhero. :-)

The reason why this isn't working:
for i in l:
if i=="E" and isinstance((i+1), int ) is True:
p = l.index(i)
print (p)
...is because 'i' contains a character from the string 'l', not an integer. You compare it with 'E' (which works), but then try to add 1 to it, which errors out.