What does the 'u' symbol mean in front of string values?

Yes in short i would like to know why am I seeing a u in front of my keys and values.

I am rendering a form. The form has check-box for the particular label and one text field for the ip address. I am creating a dictionary with keys being the label which are hardcoded in the list_key and values for the dictionary are taken from the form input (list_value). The dictionary is created but it is preceded by u for some values. here is the sample output for the dictionary:

{u'1': {'broadcast': u'on', 'arp': '', 'webserver': '', 'ipaddr': u'', 'dns': ''}}

can someone please explain what I am doing wrong. I am not getting the error when i simulate similar method in pyscripter. Any suggestions to improve the code are welcome. Thank you

#!/usr/bin/env python

import webapp2
import itertools
import cgi

form ="""
	<form method="post">
	FIREWALL 
	<br><br>
	<select name="profiles">
		<option value="1">profile 1</option>
		<option value="2">profile 2</option>
		<option value="3">profile 3</option>
	</select>
	<br><br>
	Check the box to implement the particular policy
	<br><br>

	<label> Allow Broadcast
		<input type="checkbox" name="broadcast">
	</label>
	<br><br>

	<label> Allow ARP
		<input type="checkbox" name="arp">
	</label><br><br>

	<label> Allow Web traffic from external address to internal webserver
		<input type="checkbox" name="webserver">
	</label><br><br>

	<label> Allow DNS
		<input type="checkbox" name="dns">
	</label><br><br>
	
	<label> Block particular Internet Protocol  address
		<input type="text" name="ipaddr">
	</label><br><br>

	<input type="submit">	
	</form>
"""
dictionarymain={}

class MainHandler(webapp2.RequestHandler):	
    def get(self):
        self.response.out.write(form)

    def post(self):
    	# get the parameters from the form 
    	profile = self.request.get('profiles')

    	broadcast = self.request.get('broadcast')
    	arp = self.request.get('arp')
    	webserver = self.request.get('webserver')
    	dns =self.request.get('dns')
    	ipaddr = self.request.get('ipaddr')


    	# Create a dictionary for the above parameters
    	list_value =[ broadcast , arp , webserver , dns, ipaddr ]
    	list_key =['broadcast' , 'arp' , 'webserver' , 'dns' , 'ipaddr' ]

    	#self.response.headers['Content-Type'] ='text/plain'
    	#self.response.out.write(profile)

    	# map two list to a dictionary using itertools
    	adict = dict(zip(list_key,list_value))
    	self.response.headers['Content-Type'] ='text/plain'
    	self.response.out.write(adict)

    	if profile not in dictionarymain:
    		dictionarymain[profile]= {}
    	dictionarymain[profile]= adict

    	#self.response.headers['Content-Type'] ='text/plain'
    	#self.response.out.write(dictionarymain)

    	def escape_html(s):
    		return cgi.escape(s, quote =True)



app = webapp2.WSGIApplication([('/', MainHandler)],
                              debug=True)

The 'u' in front of the string values means the string is a Unicode string. Unicode is a way to represent more characters than normal ASCII can manage. The fact that you're seeing the u means you're on Python 2 - strings are Unicode by default on Python 3, but on Python 2, the u in front distinguishes Unicode strings. The rest of this answer will focus on Python 2.

You can create a Unicode string multiple ways:

>>> u'foo'
u'foo'
>>> unicode('foo') # Python 2 only
u'foo'

But the real reason is to represent something like this (translation here):

>>> val = u'Ознакомьтесь с документацией'
>>> val
u'\u041e\u0437\u043d\u0430\u043a\u043e\u043c\u044c\u0442\u0435\u0441\u044c \u0441 \u0434\u043e\u043a\u0443\u043c\u0435\u043d\u0442\u0430\u0446\u0438\u0435\u0439'
>>> print val
Ознакомьтесь с документацией

For the most part, Unicode and non-Unicode strings are interoperable on Python 2.

There are other symbols you will see, such as the "raw" symbol r for telling a string not to interpret backslashes. This is extremely useful for writing regular expressions.

>>> 'foo\"'
'foo"'
>>> r'foo\"'
'foo\\"'

Unicode and non-Unicode strings can be equal on Python 2:

>>> bird1 = unicode('unladen swallow')
>>> bird2 = 'unladen swallow'
>>> bird1 == bird2
True

but not on Python 3:

>>> x = u'asdf' # Python 3
>>> y = b'asdf' # b indicates bytestring
>>> x == y
False

This is a feature, not a bug.

See http://docs.python.org/howto/unicode.html, specifically the 'unicode type' section.