scope, modyfing outside object from inside the method

[=?iso-8859-2?q?Marcin_St=EApnicki?=]

Hello.

I thought I understand this, but apparently I don't . I'm missing
something very basic and fundamental here, so redirecting me to the
related documentation is welcomed as well as providing working code .

Trivial example which works as expected:

x = {'a':123, 'b': 456}
y = x
x['a']=890
y

{'a': 890, 'b': 456}

Now, let's try something more sophisticated (it's not real world example,
I've made up the problem which I think illustrates my issue). Let's say
I've got such a structure:

results = [ {'a': 12, 'b': 30 },
{'a': 13, 'b': 40 } ]

I'd like to have each row and column in separate object of self-made
classes.:

class mycolumn():
def __init__(self, resultset, row, col):
self.value = resultset[row][col]
def __str__(self):
return 'Column value: %s' % self.value

class myrow():
def __init__(self):
self.container = {}
def __str__ (self):
return self.container

results = [
{'a': 12, 'b' :30 },
{'a': 13, 'b' :40 }
]

mystruct = []

for row in results:
mystruct.append ( myrow() )
for col in row:
mystruct [len(mystruct)-1].container[col] = \
mycolumn(results, results.index(row), col)

print mystruct[0].container['b'] # 12
results[0]['b'] = 50 #
print mystruct[0].container['b'] # also 12 :/

In other words, I'd like to "map" the results to myrow and mycolumn
objects, and have these new objects' values changed when I change "results".

I hope I explained it well enough . Thank you for your time.

 

[Peter Otten]

Hello.

I thought I understand this, but apparently I don't . I'm missing
something very basic and fundamental here, so redirecting me to the
related documentation is welcomed as well as providing working code .

Trivial example which works as expected:

x = {'a':123, 'b': 456}
y = x
x['a']=890
y

{'a': 890, 'b': 456}

Now, let's try something more sophisticated (it's not real world example,
I've made up the problem which I think illustrates my issue). Let's say
I've got such a structure:

results = [ {'a': 12, 'b': 30 },
{'a': 13, 'b': 40 } ]

I'd like to have each row and column in separate object of self-made
classes.:

class mycolumn():
def __init__(self, resultset, row, col):
self.value = resultset[row][col]
def __str__(self):
return 'Column value: %s' % self.value

class myrow():
def __init__(self):
self.container = {}
def __str__ (self):
return self.container

results = [
{'a': 12, 'b' :30 },
{'a': 13, 'b' :40 }
]

mystruct = []

for row in results:
mystruct.append ( myrow() )
for col in row:
mystruct [len(mystruct)-1].container[col] = \
mycolumn(results, results.index(row), col)

print mystruct[0].container['b'] # 12
results[0]['b'] = 50 #
print mystruct[0].container['b'] # also 12 :/

In other words, I'd like to "map" the results to myrow and mycolumn
objects, and have these new objects' values changed when I change "results".

Instead of copying a value, you can tell your objects where to look it up.
Your mycolumn class would then become

class MyColumn(object):
def __init__(self, resultset, row, col):
self._resultset = resultset
self._row = row
self._col = col
@property
def value(self):
return self._resultset[self._row][self._col]
def __str__(self):
return 'Column value: %s' % self.value

Peter

 

[Dustan]

@property
def value(self):
return self._resultset[self._row][self._col]

I remember a thread where someone created a version of property that
worked like this, but it's not in the standard python release, unless
it is in python 3000.

 

[Guest]

Hello.

I thought I understand this, but apparently I don't . I'm missing
something very basic and fundamental here, so redirecting me to the
related documentation is welcomed as well as providing working code .

Trivial example which works as expected:

x = {'a':123, 'b': 456}
y = x
x['a']=890
y

{'a': 890, 'b': 456}

Now, let's try something more sophisticated (it's not real world example,
I've made up the problem which I think illustrates my issue). Let's say
I've got such a structure:

results = [ {'a': 12, 'b': 30 },
{'a': 13, 'b': 40 } ]

I'd like to have each row and column in separate object of self-made
classes.:

class mycolumn():
def __init__(self, resultset, row, col):
self.value = resultset[row][col]
def __str__(self):
return 'Column value: %s' % self.value

class myrow():
def __init__(self):
self.container = {}
def __str__ (self):
return self.container

results = [
{'a': 12, 'b' :30 },
{'a': 13, 'b' :40 }
]

mystruct = []

for row in results:
mystruct.append ( myrow() )
for col in row:
mystruct [len(mystruct)-1].container[col] = \
mycolumn(results, results.index(row), col)

print mystruct[0].container['b'] # 12
results[0]['b'] = 50 #
print mystruct[0].container['b'] # also 12 :/

In other words, I'd like to "map" the results to myrow and mycolumn
objects, and have these new objects' values changed when I change "results".

I hope I explained it well enough . Thank you for your time.

Would this work for you?

class myrow():
def __init__(self, idict = {}):
self.container = idict
def __str__ (self):
return self.container.__str__()

results = [
{'a': 12, 'b' :30 },
{'a': 13, 'b' :40 }
]

mystruct = []

for row in results:
mystruct.append(myrow(row))

results[1]['b'] = 444

print results # [{'a': 12, 'b': 30}, {'a': 13, 'b': 444}]

print mystruct # does not work ok , you should probably define
# mystruct's __str__ method properly

# But, save for the __str__ thingy, the rest is ok.

for row in mystruct:
print row

# {'a': 12, 'b': 30}
# {'a': 13, 'b': 444}

HTH

 

[=?iso-8859-2?q?Marcin_St=EApnicki?=]

Dnia Mon, 24 Sep 2007 10:41:22 -0300, Ricardo Aráoz napisał(a):

Would this work for you?

Thank you both for help. Well - yes and no . It's getting more
interesting:

First, your code:

class myrow():
def __init__(self, idict = {}):
self.container = idict
def __str__ (self):
return self.container.__str__()

results = [
{'a': 12, 'b' :30 },
{'a': 13, 'b' :40 }
]

mystruct = []

for row in results:
mystruct.append(myrow(row))

results[1]['b'] = 444

print results # [{'a': 12, 'b': 30}, {'a': 13, 'b': 444}]

print mystruct # does not work ok , you should probably define
# mystruct's __str__ method properly

# But, save for the __str__ thingy, the rest is ok.

for row in mystruct:
print row

# {'a': 12, 'b': 30}
# {'a': 13, 'b': 444}

And now let's try to swap results with something else:

print id(results)

# new resultset
results = [
{'a': 112, 'b' : 130 },
{'a': 113, 'b' : 140 }
]

print id(results)
for row in mystruct:
print row

# {'a': 12, 'b': 30}
# {'a': 13, 'b': 444}

At first glance (before adding id()) it's a little bit weird. The original
object was supposedly "overwritten", but as one can see it has different
id then the new one. mystruct still holds references to old object,
though. I can handle it and just change original object, but I'm curious
if there's a way to "swap" them "on-the-fly".

Thanks one again.

 

[Gabriel Genellina]

En Wed, 26 Sep 2007 10:39:22 -0300, Marcin Stępnicki

At first glance (before adding id()) it's a little bit weird. The
original
object was supposedly "overwritten", but as one can see it has different
id then the new one. mystruct still holds references to old object,
though. I can handle it and just change original object, but I'm curious
if there's a way to "swap" them "on-the-fly".

You should read this <http://effbot.org/zone/python-objects.htm>