syntax error with python code

Question

I have this function in my class:

 def removeUserFromSessionDatabase(self, user):
      if user in self.users:
         for k in self.users.keys():
            if k == user:
               del self.users[k]
               print("Removed")

            else:
               print("user does not exist")
      else:
         print "soemthing"

now I always get error at this last else with message: SyntaxError: invalid syntax where as it should work. users is a dictionary here and there is no other method. Why am I getting this syntax error?

What python version? If 3+, this needs to be print() as your other ones are. — Michael Berkowski
– Michael Berkowski, Commented Sep 8, 2012 at 20:20
why do you do the for k in self.users.keys instead of just self.users.pop(user) in fact you can use pop even if the key doesnt exist so you can get rid of that whole if — Joran Beasley
– Joran Beasley, Commented Sep 8, 2012 at 20:20
What version of Python are you using? In Python 3, print is a function: print("Something") — Warren Weckesser
– Warren Weckesser, Commented Sep 8, 2012 at 20:21
check your code for uncorrect indentation, unclosed parentheses and some forgotten whitespace. — unddoch
– unddoch, Commented Sep 8, 2012 at 20:22
@MichaelBerkowski: the syntax error would be on the print line, then, not on the else: statement. — Martijn Pieters
– Martijn Pieters, Commented Sep 8, 2012 at 20:23

Martijn Pieters · Accepted Answer · 2012-09-08 20:21:22Z

3

Your indentation could be incorrect, most likely caused by tabs. Run python -tt scriptname.py to check.

There is otherwise no syntax error in your code that would cause this specific exception, not in the code you've given us.

answered Sep 8, 2012 at 20:21

Martijn Pieters

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4 Comments

Space Rocker Over a year ago

oh thanks, that was really the case, i just reset the indentation manually and it works now. Can you tell me a good IDE Please to work with python

Fred Foo Over a year ago

@Sara: IDLE is the default IDE for Python. Many Pythonistas work without IDEs, though, preferring an editor in conjunction with IPython.

Martijn Pieters Over a year ago

@Sara: Anything that can be configured to use only spaces instead of tabs is fine.

Joran Beasley Over a year ago

eclipse + pydev is flat out the best imho ... ninja ide is lightweight and nice ... notepad++(and/or scite) is lightweight and pretty good

Joran Beasley · Accepted Answer · 2012-09-08 20:48:23Z

3

you can simplify this alot by

def removeUserFromSessionDatabase(self, user):
      return self.users.pop(user,False)

or

def removeUserFromSessionDatabase(self, user):
      if self.users.pop(user,False):
         print "%s was deleted from group"
      else:
         print "%s is not in group"

or

def removeUserFromSessionDatabase(self, user):
      userData = self.users.pop(user,False):
      if userData: 
          #do Something
      else:
          #do something else

or lastly

def removeUserFromSessionDatabase(self, user):
      try:userData = self.users.pop(user):
      except KeyError:
          #user does not exist in dict
          pass
      print "Deleted {0}:{1} From List".format((user,userData))

apparently (per denlan and I believe it) del is fine to use

def removeUserFromSessionDatabase(self, user):
      try:
         del self.users[user]
         print "Removed user"
      except KeyError:  
         print "User does not exist" 


def alt_removeUserFromSessionDatabase(self, user):
      if user in self.users
         del self.users[user]
         print "Removed user"
      else:  
         print "User does not exist"

edited Sep 8, 2012 at 20:48

answered Sep 8, 2012 at 20:22

Joran Beasley

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9 Comments

user395760 Over a year ago

Well, except for the output. But yeah, the loop is complete nonsense. As Larry Wall put it: "Doing linear scans over an associative array is like trying to club someone to death with a loaded Uzi."

Joran Beasley Over a year ago

there now it accounts for the output :P

user395760 Over a year ago

Unfortunately, that's wrong, because .pop (1) returns the values associated with the removed key, not a boolean (and that object may be falsy) and (2) it raises a KeyError if user not in self.users rather than returning something falsy.

Joran Beasley Over a year ago

there fixed by giving default val (but you are right about the value could be false/none...but in this case it sounds like that would not be a factor

user395760 Over a year ago

Still, no need to introduce such a subtle assumption, and no need to obfuscate by putting a side effect into a condition. What the heck is wrong with checking if user in self.users and using del self.users[user] in one of the branches?

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