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Python automatically converting some strings to raw strings?

Python seems to be automatically converting strings (not just input) into raw strings. Can somebody explain what is happening here?
Python 3.7.1 (v3.7.1:260ec2c36a, Oct 20 2018, 14:57:15) [MSC v.1915 64 bit
(AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> s = '\stest'
>>> s
'\\stest'
# looks like a raw string
>>> print(s)
\stest
>>> s = '\ntest'
>>> s
'\ntest'
# this one doesn't
>>> s = '\n test'
>>> s
'\n test'
>>> s = r'\n test'
>>> s
'\\n test'
>>> print(s)
\n test
The question marked as a duplicate for this one seems to be useful, but then I do not understand why
>>> s = '\n test'
>>> s
'\n test'
>>> repr(s)
"'\\n test'"
does not get two backslashes when called, and does when repr() is called on it.

\n is a valid escape sequence and '\n' is a length 1 string (new line character). In contrast, \s is an invalid escape sequence, so Python is assuming that what you wanted there was a two character string: a backlash character plus an s character.
>>> len('\s')
2
What you saw on terminal output was just the usual representation for such a length 2 string. Note that the correct way to create the string which Python gave you back here would have been with r'\s' or with '\\s'.
>>> r'\s' == '\\s' == '\s'
True
This is a deprecated behavior. In a future version of Python, likely the next point release, your code will be a syntax error.
Since you're using v3.7.1, you could enable warnings if you want to be informed about such uses of deprecated features:
$ python -Wall
>>> '\s'
<stdin>:1: DeprecationWarning: invalid escape sequence \s
'\\s'
As for your subsequent question after the edit:
>>> s = '\n test'
>>> s # this prints the repr(s)
'\n test'
>>> repr(s) # this prints the repr(repr(s))
"'\\n test'"

How to extract a part of url from dictionary value in Python?

I have a dictionary where the key's value is
https://service-dmn1-region.com/info 4169 description
I'm interested in fetching dmn1-region from that URL part and print 4169 description as it is. So I intend to print result as:
dmn1-region :4169 description
Do you think it's possible without complex regex/regular expression. The script is in python and tried this -
import re
print re.sub('https://','',dictionary[key])
This just removes https:// part and shows result as service-dmn1-region.com/info 4169 description . But I'm not sure how to achieve the above intended way.
key-value pairs from dictionary looks like-
dictionary = {'service': 'https://service-dmn1-region.com/info 4169 description',
'service1': 'https://service1-dmn2-region2.com/info 5123 someDescription','service2': 'https://dmn1-region-service2.com/info'}
Any insights and help very much appreciated.

Given the information and the fact that you don't want to use regular expressions, you could do something like this:
dictionary = {'service': 'https://service-dmn1-region.com/info 4169 description',
'service1': 'https://service1-dmn2-region2.com/info 5123 someDescription'}
def extract(key, s):
info = '/info'
service = key + '-'
return s[s.find('service') + len(service):s.find('.com')], s[s.find(info) + len(info):].strip()
for key, value in dictionary.items():
region, info = extract(key, value)
print('{0}:{1}'.format(region, info))
Output
dmn2-region2:5123 someDescription
dmn1-region:4169 description
Note that the urls are the values of the dictionary and not the keys.

I'd use something like:
import re
for k, v in dictionary.items(): # .iteritems() for py2
print(re.sub(r"^.*?{}-([^.]+).*?(\d+)\s(.*?)$".format(k), r"\1 :\2 \3", v))
dmn1-region :4169 description
dmn2-region2 :5123 someDescription
DEMO

for values of the type https://service-dmn1-region.com/info 4169 description
you could just match on ^[^-]+-([^.]+)[^\s]+ (.*)$
[harald#localhost ~]$ python3
Python 3.6.6 (default, Jul 19 2018, 14:25:17)
[GCC 8.1.1 20180712 (Red Hat 8.1.1-5)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> val = 'https://service-dmn1-region.com/info
4169 description'
>>> res = re.match('^[^-]+-([^.]+)[^\s]+ (.*)$', val)
>>> res.group(1)
'dmn1-region'
>>> res.group(2)
'4169 description'
where ^[^-]+ matches from the start of the input (initial ^) anything that isn't an apostrophe - ([^-]+), so https://service
next you specify that there must be one apostrophe to follow ^[⁻]+- and that you wish to capture
everything that follows next that isn't a dot with ([^.]+). (as you guessed by now, precluding your pattern with ^ negates it and the pattern is written inside brackets [].
Leading us to ^[^-]+-([^.]+), next you wish ignore everything up to the next whitespace since that seperates the other values from the string so you add a pattern match for anything not whitespace (\s) leading to an extra [^\s]+, so ^[^-]+-([^.]+)[^\s]+
which you then wish to follow up by the whitespace seperator (if expect more than 1 whitespace you could use \s* instead of an actual space) and you add a final catch-all capture pattern (.*), which would capture 4169 description (the dot stands for all characters here) until the end of the input $ leading you to ^[^-]+-([^.]+)[^\s]+ (.*)$.

Removing non integers from a grep obtained string w/ Python and Bash

I am using grep to grab the text out of a file:
NELECT = 44.0000 total number of electrons,
and I need to save the number as a variable. I have tried a handful of methods I have found here such as using filters and findall. For some reason I can only get it to separate one zero.
So far the code looks like this:
wd=os.getcwd()
electrons=str(os.system("grep 'NELECT' "+wd+"/OUTCAR"))
VBM=(re.findall('\d+', electrons))
print VBM
And in return I get ['0'].

The result of os.system is the exit status of the command, not the output of the command -- see https://docs.python.org/3/library/os.html#os.system
$ cat OUTCAR
NELECT = 44.0000 total number of electrons,
$ python
Python 2.7.12 (default, Dec 4 2017, 14:50:18)
[GCC 5.4.0 20160609] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> result = os.system("grep 'NELECT' "+os.getcwd()+"/OUTCAR")
NELECT = 44.0000 total number of electrons,
>>> result
0
The "NELECT" line was just printed by grep to stdout, but not captured in the result variable
>>> from subprocess import check_output
>>> result2 = check_output(["grep", "NELECT", os.getcwd()+"/OUTCAR"])
>>> result2
'NELECT = 44.0000 total number of electrons,\n'
>>> import re
>>> re.findall(r'\d+', result2)
['44', '0000']
Or, don't call out to grep, read the file yourself
>>> import os
>>> import re
>>> with open(os.getcwd() + "/OUTCAR") as f:
... for line in f:
... if "NELECT" in line:
... digits = re.findall(r'\d+', line)
... break
...
>>> digits
['44', '0000']
Or, maybe don't use a regular expression:
>>> words = line.split()
>>> words[2]
'44.0000'
>>> int(float(words[2]))
44

Are you sure that electrons has output specified? For me this regex returns list with two elements: ['44', '000'] and that's expected behavior. So most probably there is something wrong with grep call.
Your regex won't retrieve whole 44.000 as \d+ catches only continuous digit strings, no dot symbols. To get whole number use something like \b\d+\.\d+\b which means: any word (\b means word beginning/ending, dot must be escaped as . in regex matches any character) that contains at least 1 digit, dot and at least 1 more digit. If dot is optional, then something like this: \b(\d+(?:\.\d+)?)\b ((?:) creates group that will not be captured so your output will still be single element list).
Note that re.findall will return list of string matches. To retrieve number from first match: float(VBM[0])
Edit. Forgot to add: avoid using print statement, it works oddly with tuples and is completely removed in Python 3. Python 2 support ends in 2020 so it's better to prepare. You can replace print statement with Python 3 print function by adding from __future__ import print_function at the file beginning.

Python regular expression gives unexpected result

I'm trying to create an svn pre-commit hook, but can't get my regular expression to work as expected. It should print False for messages that do not look like "DEV-5 | some message". Why do I get True here?
Python 2.7.1+ (r271:86832, Apr 11 2011, 18:05:24)
[GCC 4.5.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import re
>>> p = re.compile("^\[[A-Z]+-[0-9]+\] | .+$", re.DOTALL)
>>> message = "test message"
>>> match = p.search(message)
>>> bool(match)
True

>>> p = re.compile("^[A-Z]+-[0-9]+ \| .+$", re.DOTALL)
>>> print p.search("test message")
None
>>> print p.search("DEV-5 | some message")
<_sre.SRE_Match object at 0x800eb78b8>
you don't need \[ and \]
you need to escape |

The culprit is the trailing " | .+$" which is matching ' message' as an alternative to the first regex. As Roman pointed out you meant to match literal '|' so you have to escape it as '\|'.
To see what was being matched, you can do:
print match.group()
' message'
(By the way, a faster non-regex way to only handle lines containing vertical bar would use line.split('|'):
for line in ...:
parts = line.split('|',1)
if len(parts)==1: continue
(code,mesg) = parts

I haven't run the code, but I suspect that the part after the alternative (|) in your regexp matches any nonempty string starting with a space, in this case it's " message".

How do I keep Python print from adding newlines or spaces? [duplicate]

This question already has answers here:
How to print without a newline or space
(26 answers)
Closed 5 years ago.
In python, if I say
print 'h'
I get the letter h and a newline. If I say
print 'h',
I get the letter h and no newline. If I say
print 'h',
print 'm',
I get the letter h, a space, and the letter m. How can I prevent Python from printing the space?
The print statements are different iterations of the same loop so I can't just use the + operator.

In Python 3, use
print('h', end='')
to suppress the endline terminator, and
print('a', 'b', 'c', sep='')
to suppress the whitespace separator between items. See the documentation for print

import sys
sys.stdout.write('h')
sys.stdout.flush()
sys.stdout.write('m')
sys.stdout.flush()
You need to call sys.stdout.flush() because otherwise it will hold the text in a buffer and you won't see it.

Greg is right-- you can use sys.stdout.write
Perhaps, though, you should consider refactoring your algorithm to accumulate a list of <whatevers> and then
lst = ['h', 'm']
print "".join(lst)

Or use a +, i.e.:
>>> print 'me'+'no'+'likee'+'spacees'+'pls'
menolikeespaceespls
Just make sure all are concatenate-able objects.

Python 2.5.2 (r252:60911, Sep 27 2008, 07:03:14)
[GCC 4.3.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> print "hello",; print "there"
hello there
>>> print "hello",; sys.stdout.softspace=False; print "there"
hellothere
But really, you should use sys.stdout.write directly.

For completeness, one other way is to clear the softspace value after performing the write.
import sys
print "hello",
sys.stdout.softspace=0
print "world",
print "!"
prints helloworld !
Using stdout.write() is probably more convenient for most cases though.

This may look stupid, but seems to be the simplest:
print 'h',
print '\bm'

Regain control of your console! Simply:
from __past__ import printf
where __past__.py contains:
import sys
def printf(fmt, *varargs):
sys.stdout.write(fmt % varargs)
then:
>>> printf("Hello, world!\n")
Hello, world!
>>> printf("%d %d %d\n", 0, 1, 42)
0 1 42
>>> printf('a'); printf('b'); printf('c'); printf('\n')
abc
>>>
Bonus extra: If you don't like print >> f, ..., you can extending this caper to fprintf(f, ...).

I am not adding a new answer. I am just putting the best marked answer in a better format.
I can see that the best answer by rating is using sys.stdout.write(someString). You can try this out:
import sys
Print = sys.stdout.write
Print("Hello")
Print("World")
will yield:
HelloWorld
That is all.

In python 2.6:
>>> print 'h','m','h'
h m h
>>> from __future__ import print_function
>>> print('h',end='')
h>>> print('h',end='');print('m',end='');print('h',end='')
hmh>>>
>>> print('h','m','h',sep='');
hmh
>>>
So using print_function from __future__ you can set explicitly the sep and end parameteres of print function.

You can use print like the printf function in C.
e.g.
print "%s%s" % (x, y)

print("{0}{1}{2}".format(a, b, c))

sys.stdout.write is (in Python 2) the only robust solution. Python 2 printing is insane. Consider this code:
print "a",
print "b",
This will print a b, leading you to suspect that it is printing a trailing space. But this is not correct. Try this instead:
print "a",
sys.stdout.write("0")
print "b",
This will print a0b. How do you explain that? Where have the spaces gone?
I still can't quite make out what's really going on here. Could somebody look over my best guess:
My attempt at deducing the rules when you have a trailing , on your print:
First, let's assume that print , (in Python 2) doesn't print any whitespace (spaces nor newlines).
Python 2 does, however, pay attention to how you are printing - are you using print, or sys.stdout.write, or something else? If you make two consecutive calls to print, then Python will insist on putting in a space in between the two.

print('''first line \
second line''')
it will produce
first line second line

import sys
a=raw_input()
for i in range(0,len(a)):
sys.stdout.write(a[i])