Re: Problem/bug with class definition inside function definition

[Gregory Ewing]

Alexey Muranov wrote:

   x = 42

   class C:
   x = x  # Works


I'd say it kind of works by accident, and is not really an
intended feature.

if Python does not allow to refer "simultaneously" to 
variables from different scopes if they have the same name.


It seems perfectly reasonable to me to have to use different
names to refer to different things in the same context. :-)

--
Greg
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Re: Problem/bug with class definition inside function definition

[Ned Batchelder]

On 5/8/18 3:55 AM, Alexey Muranov wrote:
Sorry, i was confused.  I would say that this mostly works as 
expected, though the difference between


   x = 42

   class C:
   x = x  # Works

and

   def f2(a):
   class D:
   a = a  # Does not work <
   return D

is still surprising to me.

Otherwise, probably the solution with

   def f(a):
   _a = a
   class D:
   a = _a
   return D

is good enough, if Python does not allow to refer "simultaneously" to 
variables from different scopes if they have the same name.


Alexey.


I'm curious to see the real code you're writing that uses this style of 
class creation.  It feels like there might be an easier way to achieve 
your goal.


--Ned.



On Tue, 8 May, 2018 at 12:21 AM, Alexey Muranov 
 wrote:

To be more exact, i do see a few workarounds, for example:


   def f4(a):
   b = a
   class D:
   a = b  # Works
   return D

But this is not what i was hoping for.

Alexey.

On Tue, 8 May, 2018 at 12:02 AM, Alexey Muranov 
 wrote:
I have discovered the following bug or problem: it looks like i am 
forced to choose different names for class attributes and function 
arguments, and i see no workaround.  Am i missing some special 
syntax feature ?


Alexey.

---
x = 42

class C1:
   y = x  # Works

class C2:
   x = x  # Works

# ---
def f1(a):
   class D:
   b = a  # Works
   return D

def f2(a):
   class D:
   a = a  # Does not work <
   return D

def f3(a):
   class D:
   nonlocal a
   a = a  # Does not work either <
   return D

# ---
def g1(a):
   def h():
   b = a  # Works
   return b
   return h

def g2(a):
   def h():
   a = a  # Does not work (as expected)
   return a
   return h

def g3(a):
   def h():
   nonlocal a
   a = a  # Works
   return a
   return h

# ---
if __name__ == "__main__":
   assert C1.y == 42
   assert C2.x == 42

   assert f1(13).b == 13

   try:
   f2(13)  # NameError
   except NameError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
    '{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   try:
   f3(13).a  # AttributeError
   except AttributeError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
    '{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g1(13)() == 13

   try:
   g2(13)()  # UnboundLocalError
   except UnboundLocalError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
    '{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g3(13)() == 13







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Re: Problem/bug with class definition inside function definition

[Alexey Muranov]

Sorry, i was confused.  I would say that this mostly works as expected, 
though the difference between


   x = 42

   class C:
   x = x  # Works

and

   def f2(a):
   class D:
   a = a  # Does not work <
   return D

is still surprising to me.

Otherwise, probably the solution with

   def f(a):
   _a = a
   class D:
   a = _a
   return D

is good enough, if Python does not allow to refer "simultaneously" to 
variables from different scopes if they have the same name.


Alexey.


On Tue, 8 May, 2018 at 12:21 AM, Alexey Muranov 
 wrote:

To be more exact, i do see a few workarounds, for example:


   def f4(a):
   b = a
   class D:
   a = b  # Works
   return D

But this is not what i was hoping for.

Alexey.

On Tue, 8 May, 2018 at 12:02 AM, Alexey Muranov 
 wrote:
I have discovered the following bug or problem: it looks like i am 
forced to choose different names for class attributes and function 
arguments, and i see no workaround.  Am i missing some special 
syntax feature ?


Alexey.

---
x = 42

class C1:
   y = x  # Works

class C2:
   x = x  # Works

# ---
def f1(a):
   class D:
   b = a  # Works
   return D

def f2(a):
   class D:
   a = a  # Does not work <
   return D

def f3(a):
   class D:
   nonlocal a
   a = a  # Does not work either <
   return D

# ---
def g1(a):
   def h():
   b = a  # Works
   return b
   return h

def g2(a):
   def h():
   a = a  # Does not work (as expected)
   return a
   return h

def g3(a):
   def h():
   nonlocal a
   a = a  # Works
   return a
   return h

# ---
if __name__ == "__main__":
   assert C1.y == 42
   assert C2.x == 42

   assert f1(13).b == 13

   try:
   f2(13)  # NameError
   except NameError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   try:
   f3(13).a  # AttributeError
   except AttributeError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g1(13)() == 13

   try:
   g2(13)()  # UnboundLocalError
   except UnboundLocalError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g3(13)() == 13





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Re: Problem/bug with class definition inside function definition

[Gregory Ewing]

Python 3.5.1 (default, Jun  1 2016, 13:15:26)
[GCC 4.2.1 (Apple Inc. build 5664)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> def f(a):
...  class D:
...   pass
...  D.a = a
...  return D
...
>>> c = f(42)
>>> c
.D'>
>>> c.a
42

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Re: Problem/bug with class definition inside function definition

[Alexey Muranov]

To be more exact, i do see a few workarounds, for example:


   def f4(a):
   b = a
   class D:
   a = b  # Works
   return D

But this is not what i was hoping for.

Alexey.

On Tue, 8 May, 2018 at 12:02 AM, Alexey Muranov 
 wrote:
I have discovered the following bug or problem: it looks like i am 
forced to choose different names for class attributes and function 
arguments, and i see no workaround.  Am i missing some special syntax 
feature ?


Alexey.

---
x = 42

class C1:
   y = x  # Works

class C2:
   x = x  # Works

# ---
def f1(a):
   class D:
   b = a  # Works
   return D

def f2(a):
   class D:
   a = a  # Does not work <
   return D

def f3(a):
   class D:
   nonlocal a
   a = a  # Does not work either <
   return D

# ---
def g1(a):
   def h():
   b = a  # Works
   return b
   return h

def g2(a):
   def h():
   a = a  # Does not work (as expected)
   return a
   return h

def g3(a):
   def h():
   nonlocal a
   a = a  # Works
   return a
   return h

# ---
if __name__ == "__main__":
   assert C1.y == 42
   assert C2.x == 42

   assert f1(13).b == 13

   try:
   f2(13)  # NameError
   except NameError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   try:
   f3(13).a  # AttributeError
   except AttributeError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g1(13)() == 13

   try:
   g2(13)()  # UnboundLocalError
   except UnboundLocalError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g3(13)() == 13



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Problem/bug with class definition inside function definition

[Alexey Muranov]

I have discovered the following bug or problem: it looks like i am 
forced to choose different names for class attributes and function 
arguments, and i see no workaround.  Am i missing some special syntax 
feature ?


Alexey.

---
x = 42

class C1:
   y = x  # Works

class C2:
   x = x  # Works

# ---
def f1(a):
   class D:
   b = a  # Works
   return D

def f2(a):
   class D:
   a = a  # Does not work <
   return D

def f3(a):
   class D:
   nonlocal a
   a = a  # Does not work either <
   return D

# ---
def g1(a):
   def h():
   b = a  # Works
   return b
   return h

def g2(a):
   def h():
   a = a  # Does not work (as expected)
   return a
   return h

def g3(a):
   def h():
   nonlocal a
   a = a  # Works
   return a
   return h

# ---
if __name__ == "__main__":
   assert C1.y == 42
   assert C2.x == 42

   assert f1(13).b == 13

   try:
   f2(13)  # NameError
   except NameError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   try:
   f3(13).a  # AttributeError
   except AttributeError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g1(13)() == 13

   try:
   g2(13)()  # UnboundLocalError
   except UnboundLocalError:
   pass
   except Exception as e:
   raise Exception( 'Unexpected exception raised: '
'{}'.format(type(e).__name__) )
   else:
   raise Exception('No exception')

   assert g3(13)() == 13

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