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Date: Wed, 18 Mar 2015 03:57:12 +0000
From: MRAB <python@mrabarnett.plus.com>
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To: python-list@python.org
Subject: Re: UnboundLocalError in TKinter, SQLAlchemy script.
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On 2015-03-18 02:41, Chris Kavanagh wrote:
> I have a simple script that takes user input (for an Employee) such as
> name, age, etc then puts in an sqlite3 database. The script worked fine
> until I realized one problem. The age input field is defined in
> SQLAlchemy as an Integer, so if a user inputs a string instead of a
> number in that field, an error will occur (in IDLE). . .
>
> So, I put a try: except clause in the code for the age field in the
> add_data method. . .
> try:
>              age = self.age_var.get()
>          except ValueError:
>              showinfo("Error:", "Please Enter A Number In Age Field.")
>
> If the user inputs a string (instead of an Int) the showinfo dialogue
> box opens as it should, but when the user clicks "ok" in the box, I get
> the error "UnboundLocalError: local variable 'age' referenced before
> assignment". I tried using a default value above the try: except clause
> (age=0), which corrects the error, but causes "0" to be saved in the
> database instead of letting the user choose another value. I want to
> figure why I get the error (with the try: except clause) and what
> exactly to do about it. Thanks in advance for any help!
>
> Here's the original code (without the try: except clause above). . .Just
> put the try: except clause in the age variable in the add_data method as
> shown above to get the error.
>
[snip]

>
>      def add_data(self):
>          name = self.name_var.get()
>          age = self.age_var.get()
>          addr = self.address_var.get()
>          city = self.city_var.get()
>          state = self.state_var.get()
>          zip = self.zip_var.get()
>          ssn = self.ssn_var.get()
>          phone = self.phone_var.get()
>          cell = self.cell_var.get()
>          # create new Employee in .db
>          new_person = Employee(name=name, age=age, address=addr,
> city=city, state=state, zip=zip, ssn=ssn, phone=phone, cell=cell)
>          session.add(new_person)
>          session.commit()
>          session.close()
>          self.callback()
>          return
>
Try stepping through the method in your head.

What happens if the user enters a non-number? A ValueError exception
occurs. You catch that, show a dialog, but then continue on with the
remainder of the method.

Because of the exception, you haven't assigned to 'age', hence the
UnboundLocalError exception.

If you assign a default value to age, it'll continue on to where you
put it into the database.

Why not just return from the method after showing the dialog?