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

Question

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) 

Answer 1

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 

Answer 2

This is a feature, not a bug.

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