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How to know the name of a classs loade like parameter on other class - Pyhton [duplicate]

This question already has answers here:
Getting the name of a variable as a string
(32 answers)
Closed 4 months ago.
Is it possible to get the original variable name of a variable passed to a function? E.g.
foobar = "foo"
def func(var):
print var.origname
So that:
func(foobar)
Returns:
>>foobar
EDIT:
All I was trying to do was make a function like:
def log(soup):
f = open(varname+'.html', 'w')
print >>f, soup.prettify()
f.close()
.. and have the function generate the filename from the name of the variable passed to it.
I suppose if it's not possible I'll just have to pass the variable and the variable's name as a string each time.

EDIT: To make it clear, I don't recommend using this AT ALL, it will break, it's a mess, it won't help you in any way, but it's doable for entertainment/education purposes.
You can hack around with the inspect module, I don't recommend that, but you can do it...
import inspect
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.getframeinfo(frame[0]).code_context[0].strip()
args = string[string.find('(') + 1:-1].split(',')
names = []
for i in args:
if i.find('=') != -1:
names.append(i.split('=')[1].strip())
else:
names.append(i)
print names
def main():
e = 1
c = 2
foo(e, 1000, b = c)
main()
Output:
['e', '1000', 'c']

To add to Michael Mrozek's answer, you can extract the exact parameters versus the full code by:
import re
import traceback
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
vars_name = re.compile(r'\((.*?)\).*$').search(code).groups()[0]
print vars_name
return
foobar = "foo"
func(foobar)
# PRINTS: foobar

Looks like Ivo beat me to inspect, but here's another implementation:
import inspect
def varName(var):
lcls = inspect.stack()[2][0].f_locals
for name in lcls:
if id(var) == id(lcls[name]):
return name
return None
def foo(x=None):
lcl='not me'
return varName(x)
def bar():
lcl = 'hi'
return foo(lcl)
bar()
# 'lcl'
Of course, it can be fooled:
def baz():
lcl = 'hi'
x='hi'
return foo(lcl)
baz()
# 'x'
Moral: don't do it.

Another way you can try if you know what the calling code will look like is to use traceback:
def func(var):
stack = traceback.extract_stack()
filename, lineno, function_name, code = stack[-2]
code will contain the line of code that was used to call func (in your example, it would be the string func(foobar)). You can parse that to pull out the argument

You can't. It's evaluated before being passed to the function. All you can do is pass it as a string.

#Ivo Wetzel's answer works in the case of function call are made in one line, like
e = 1 + 7
c = 3
foo(e, 100, b=c)
In case that function call is not in one line, like:
e = 1 + 7
c = 3
foo(e,
1000,
b = c)
below code works:
import inspect, ast
def foo(a, f, b):
frame = inspect.currentframe()
frame = inspect.getouterframes(frame)[1]
string = inspect.findsource(frame[0])[0]
nodes = ast.parse(''.join(string))
i_expr = -1
for (i, node) in enumerate(nodes.body):
if hasattr(node, 'value') and isinstance(node.value, ast.Call)
and hasattr(node.value.func, 'id') and node.value.func.id == 'foo' # Here goes name of the function:
i_expr = i
break
i_expr_next = min(i_expr + 1, len(nodes.body)-1)
lineno_start = nodes.body[i_expr].lineno
lineno_end = nodes.body[i_expr_next].lineno if i_expr_next != i_expr else len(string)
str_func_call = ''.join([i.strip() for i in string[lineno_start - 1: lineno_end]])
params = str_func_call[str_func_call.find('(') + 1:-1].split(',')
print(params)
You will get:
[u'e', u'1000', u'b = c']
But still, this might break.

You can use python-varname package
from varname import nameof
s = 'Hey!'
print (nameof(s))
Output:
s
Package below:
https://github.com/pwwang/python-varname

For posterity, here's some code I wrote for this task, in general I think there is a missing module in Python to give everyone nice and robust inspection of the caller environment. Similar to what rlang eval framework provides for R.
import re, inspect, ast
#Convoluted frame stack walk and source scrape to get what the calling statement to a function looked like.
#Specifically return the name of the variable passed as parameter found at position pos in the parameter list.
def _caller_param_name(pos):
#The parameter name to return
param = None
#Get the frame object for this function call
thisframe = inspect.currentframe()
try:
#Get the parent calling frames details
frames = inspect.getouterframes(thisframe)
#Function this function was just called from that we wish to find the calling parameter name for
function = frames[1][3]
#Get all the details of where the calling statement was
frame,filename,line_number,function_name,source,source_index = frames[2]
#Read in the source file in the parent calling frame upto where the call was made
with open(filename) as source_file:
head=[source_file.next() for x in xrange(line_number)]
source_file.close()
#Build all lines of the calling statement, this deals with when a function is called with parameters listed on each line
lines = []
#Compile a regex for matching the start of the function being called
regex = re.compile(r'\.?\s*%s\s*\(' % (function))
#Work backwards from the parent calling frame line number until we see the start of the calling statement (usually the same line!!!)
for line in reversed(head):
lines.append(line.strip())
if re.search(regex, line):
break
#Put the lines we have groked back into sourcefile order rather than reverse order
lines.reverse()
#Join all the lines that were part of the calling statement
call = "".join(lines)
#Grab the parameter list from the calling statement for the function we were called from
match = re.search('\.?\s*%s\s*\((.*)\)' % (function), call)
paramlist = match.group(1)
#If the function was called with no parameters raise an exception
if paramlist == "":
raise LookupError("Function called with no parameters.")
#Use the Python abstract syntax tree parser to create a parsed form of the function parameter list 'Name' nodes are variable names
parameter = ast.parse(paramlist).body[0].value
#If there were multiple parameters get the positional requested
if type(parameter).__name__ == 'Tuple':
#If we asked for a parameter outside of what was passed complain
if pos >= len(parameter.elts):
raise LookupError("The function call did not have a parameter at postion %s" % pos)
parameter = parameter.elts[pos]
#If there was only a single parameter and another was requested raise an exception
elif pos != 0:
raise LookupError("There was only a single calling parameter found. Parameter indices start at 0.")
#If the parameter was the name of a variable we can use it otherwise pass back None
if type(parameter).__name__ == 'Name':
param = parameter.id
finally:
#Remove the frame reference to prevent cyclic references screwing the garbage collector
del thisframe
#Return the parameter name we found
return param

If you want a Key Value Pair relationship, maybe using a Dictionary would be better?
...or if you're trying to create some auto-documentation from your code, perhaps something like Doxygen (http://www.doxygen.nl/) could do the job for you?

I wondered how IceCream solves this problem. So I looked into the source code and came up with the following (slightly simplified) solution. It might not be 100% bullet-proof (e.g. I dropped get_text_with_indentation and I assume exactly one function argument), but it works well for different test cases. It does not need to parse source code itself, so it should be more robust and simpler than previous solutions.
#!/usr/bin/env python3
import inspect
from executing import Source
def func(var):
callFrame = inspect.currentframe().f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
expression = source.asttokens().get_text(callNode.args[0])
print(expression, '=', var)
i = 1
f = 2.0
dct = {'key': 'value'}
obj = type('', (), {'value': 42})
func(i)
func(f)
func(s)
func(dct['key'])
func(obj.value)
Output:
i = 1
f = 2.0
s = string
dct['key'] = value
obj.value = 42
Update: If you want to move the "magic" into a separate function, you simply have to go one frame further back with an additional f_back.
def get_name_of_argument():
callFrame = inspect.currentframe().f_back.f_back
callNode = Source.executing(callFrame).node
source = Source.for_frame(callFrame)
return source.asttokens().get_text(callNode.args[0])
def func(var):
print(get_name_of_argument(), '=', var)

If you want to get the caller params as in #Matt Oates answer answer without using the source file (ie from Jupyter Notebook), this code (combined from #Aeon answer) will do the trick (at least in some simple cases):
def get_caller_params():
# get the frame object for this function call
thisframe = inspect.currentframe()
# get the parent calling frames details
frames = inspect.getouterframes(thisframe)
# frame 0 is the frame of this function
# frame 1 is the frame of the caller function (the one we want to inspect)
# frame 2 is the frame of the code that calls the caller
caller_function_name = frames[1][3]
code_that_calls_caller = inspect.findsource(frames[2][0])[0]
# parse code to get nodes of abstract syntact tree of the call
nodes = ast.parse(''.join(code_that_calls_caller))
# find the node that calls the function
i_expr = -1
for (i, node) in enumerate(nodes.body):
if _node_is_our_function_call(node, caller_function_name):
i_expr = i
break
# line with the call start
idx_start = nodes.body[i_expr].lineno - 1
# line with the end of the call
if i_expr < len(nodes.body) - 1:
# next expression marks the end of the call
idx_end = nodes.body[i_expr + 1].lineno - 1
else:
# end of the source marks the end of the call
idx_end = len(code_that_calls_caller)
call_lines = code_that_calls_caller[idx_start:idx_end]
str_func_call = ''.join([line.strip() for line in call_lines])
str_call_params = str_func_call[str_func_call.find('(') + 1:-1]
params = [p.strip() for p in str_call_params.split(',')]
return params
def _node_is_our_function_call(node, our_function_name):
node_is_call = hasattr(node, 'value') and isinstance(node.value, ast.Call)
if not node_is_call:
return False
function_name_correct = hasattr(node.value.func, 'id') and node.value.func.id == our_function_name
return function_name_correct
You can then run it as this:
def test(*par_values):
par_names = get_caller_params()
for name, val in zip(par_names, par_values):
print(name, val)
a = 1
b = 2
string = 'text'
test(a, b,
string
)
to get the desired output:
a 1
b 2
string text

Since you can have multiple variables with the same content, instead of passing the variable (content), it might be safer (and will be simpler) to pass it's name in a string and get the variable content from the locals dictionary in the callers stack frame. :
def displayvar(name):
import sys
return name+" = "+repr(sys._getframe(1).f_locals[name])

If it just so happens that the variable is a callable (function), it will have a __name__ property.
E.g. a wrapper to log the execution time of a function:
def time_it(func, *args, **kwargs):
start = perf_counter()
result = func(*args, **kwargs)
duration = perf_counter() - start
print(f'{func.__name__} ran in {duration * 1000}ms')
return result

Update text in real time by calling two functions Pygame

I have program that takes input from the user and displays multiple variations of the input using the Population() function. The store_fit function adds these different variations to a list then deletes them so that the list is only populated with one variation at a time.
I want to be able to get the variation from the list and use it to update my text. However, my program only updates the text after the Population function is completed. How could I run the Population function and update my text simultaneously?
code:
fit = []
...
def store_fit(fittest): # fittest is each variation from Population
clear.fit()
fit.append(fittest)
...
pg.init()
...
done = False
while not done:
...
if event.key == pg.K_RETURN:
print(text)
target = text
Population(1000) #1000 variations
store_fit(value)
# I want this to run at the same time as Population
fittest = fit[0]
...
top_sentence = font.render(("test: " + fittest), 1, pg.Color('lightskyblue3'))
screen.blit(top_sentence, (400, 400))

I recommend to make Population a generator function. See The Python yield keyword explained:
def Populate(text, c):
for i in range(c):
# compute variation
# [...]
yield variation
Create an iterator and use next() to retrieve the next variation in the loop, so you can print every single variation:
populate_iter = Populate(text, 1000)
final_variation = None
while not done:
next_variation = next(populate_iter, None)
if next_variation :
final_variation = next_variation
# print current variation
# [...]
else:
done = True
Edit according to the comment:
In order to keep my question simple, I didn't mention that Population, was a class [...]
Of course Populate can be a class, too. I this case you've to implement the object.__iter__(self) method. e.g.:
class Populate:
def __init__(self, text, c):
self.text = text
self.c = c
def __iter__(self):
for i in range(self.c):
# compute variation
# [...]
yield variation
Create an iterator by iter(). e.g.:
populate_iter = iter(Populate(text, 1000))
final_variation = None
while not done:
next_variation = next(populate_iter, None)
if next_variation :
final_variation = next_variation
# print current variation
# [...]
else:
done = True

Why isn't self working in my code

I'm writing some code to create a toolbar that edits a map in ArcMap and I'm having some issues with getting variable values from other functions inside other classes that I'm using.
All the functions are predefined so I can't change the int arguments or the code will throw an error. I checked the dir() and none of the variables I define using self are in the functions. I don't think I've made a syntax error and the code inside the other classes works correctly.
Here is my code:
import arcpy
import math
import pythonaddins
class findingCoordinates(object):
"""Implementation for leetScripts_addin.tool (Tool)"""
def __init__(self):
self.enabled = True
self.shape = "NONE"
def onMouseDownMap(self, x, y, button, shift):
print "onMouseDowMap executing"
#this is where I declared the first two variables using self
self.x = x
self.y = y
print "Selected point is at %r, %r" % (self.x, self.y)
pass
class squareFeetInput(object):
"""Implementation for leetScripts_addin.combobox (ComboBox)"""
def __init__(self):
self.editable = True
self.enabled = True
#self.dropdownWidth = 'WWWWWW'
self.width = 'WWWWWW'
def onEditChange(self, text):
squareFeet = text
#this is the other variable I defined that I need to use later
self.buffDist = (math.sqrt(float(squareFeet))/2)
print "Square size: %r ft^2 Buffer Distance: %r ft^2" % (squareFeet,self.buffDist)
print "self.buffdist is a %r type" % self.buffDist
return self.buffDist
pass
class buildingTool(object):
"""Implementation for leetScripts_addin.button (Button)"""
def __init__(self):
self.enabled = True
self.checked = False
def onClick(self):
print "building tool is executing"
#shows im_self, but no x or y
print "%r" % dir(findingCoordinates.onMouseDownMap)
# Get arguments:
# Input point feature class
# Output polygon feature class
# Buffer distance
# Boolean type: Maintain fields and field values of the input in the output
#This is where the problem is. I can't get these values from the previous functions.
inPoints = (findingCoordinates.onMouseDownMap.x,findingCoordinates.onMouseDownMap.y)
outPolys = "U:\JackBuildingFootprints.gdb\BuildingFootprintsCopy"
bufDist = squareFeetInput.buffDist
keepFields = true
# Prepare the output based on whether field and field values are desired in the output
#
if keepFields:
# Create empty output polygon feature class that includes fields of the input
#
arcpy.CreateFeatureClass(os.path.dirname(outPolys), os.path.basename(outPolys), "POLYGON",
inPoints, "", "", inPoints)
# Create a short list of fields to ignore when moving fields values from
# input to output
#
ignoreFields = []
# Use Describe properties to identify the shapeFieldName and OIDFieldName
#
desc = arcpy.Describe(inPoints)
ignoreFields.append(desc.shapeFieldName)
ignoreFields.append(desc.OIDFieldName)
# Create a list of fields to use when moving field values from input to output
#
fields = arcpy.ListFields(inPoints)
fieldList = []
for field in fields:
if field.name not in ignoreFields:
fieldList.append(field.name)
else:
# Create empty output polygon feature class without fields of the input
#
arcpy.CreateFeatureclass(os.path.dirname(outPolys), os.path.basename(outPolys), "POLYGON",
"", "", "", inPoints)
# Open searchcursor
#
inRows = arcpy.SearchCursor(inPoints)
# Open insertcursor
#
outRows = arcpy.InsertCursor(outPolys)
# Create point and array objects
#
pntObj = arcpy.Point()
arrayObj = arcpy.Array()
for inRow in inRows: # One output feature for each input point feature
inShape = inRow.shape
pnt = inShape.getPart(0)
# Need 5 vertices for square buffer: upper right, upper left, lower left,
# lower right, upper right. Add and subtract distance from coordinates of
# input point as appropriate.
for vertex in [0,1,2,3,4]:
pntObj.ID = vertex
if vertex in [0,3,4]:
pntObj.X = pnt.X + bufDist
else:
pntObj.X = pnt.X - bufDist
if vertex in [0,1,5]:
pntObj.Y = pnt.Y + bufDist
else:
pntObj.Y = pnt.Y - bufDist
arrayObj.add(pntObj)
# Create new row for output feature
#
feat = outRows.newRow()
# Shift attributes from input to output
#
if keepFields == "true":
for fieldName in fieldList:
feat.setValue(fieldName, inRow.getValue(fieldName))
# Assign array of points to output feature
#
feat.shape = arrayObj
# Insert the feature
#
outRows.insertRow(feat)
# Clear array of points
#
arrayObj.removeAll()
# Delete inputcursor
#
del outRows
pass
What am I doing wrong? Is this one of the rare occasions where I should use a global variable? Why is the directory not showing the variables I defined using self?
Edit:
I made this post a while ago and I just wanted to clear some things up now that I know more.
First:
This is code that is designed to be use with python_add_in. Python add in creates a toolbar based on some parameters you give it when you set it up, and whatever python code you put into a template it makes as a result of those parameters. That essentially means that all of the classes in the script above are events that occur when buttons and other toolbar objects are clicked or used in the toolbar.
Second:
The solution to this problem actually isn't in the accepted answer, my bad.
The root cause of the problem is that I was using class names that I declared in my script, findingCoordinates for example. python_add_in doesn't recognize these class names as the names of the classes it expects to receive based on the template you fill out before you start coding.
With that in mind, the issue was that I was trying to call classes that just didn't exist as far as python_add_in was concerned. The solution is to just go ahead and use the class names python_add_in tool expects you to use. These names are in the docstring located below the class definition so where I have findingCoordinates I should have Tool.
I hope this helps.

self refers to an instance of the class that you've defined, so to access those values, you need to create an instance of the class, call the method, and then access the values from the instance.
For example:
In [9]: %paste
class findingCoordinates(object):
"""Implementation for leetScripts_addin.tool (Tool)"""
def __init__(self):
self.enabled = True
self.shape = "NONE"
def onMouseDownMap(self, x, y, button, shift):
print "onMouseDowMap executing"
#this is where I declared the first two variables using self
self.x = x
self.y = y
print "Selected point is at %r, %r" % (self.x, self.y)
pass
## -- End pasted text --
In [10]: f = findingCoordinates()
In [11]: f.onMouseDownMap(x=1, y=2, button="button", shift="shift")
onMouseDowMap executing
Selected point is at 1, 2
In [12]: f.x
Out[12]: 1
In [13]: f.y
Out[13]: 2
EDIT: It seems like you've had some confusion about scoping/namespaces as well. There's no x or y defined globally; they just exist within the class instances. That will also allow you to have separate x and y values for different instances of the class.
In [14]: x
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-14-401b30e3b8b5> in <module>()
----> 1 x
NameError: name 'x' is not defined
In [15]: y
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-15-009520053b00> in <module>()
----> 1 y
NameError: name 'y' is not defined
In [16]: g = findingCoordinates()
In [17]: g.onMouseDownMap(100,200,0,0)
onMouseDowMap executing
Selected point is at 100, 200
In [18]: f.x, f.y
Out[18]: (1, 2)
In [19]: g.x, g.y
Out[19]: (100, 200)

Proper handling of spark broadcast variables in a Python class

I've been implementing a model with spark via a python class. I had some headaches calling class methods on a RDD defined in the class (see this question for details), but finally have made some progress. Here is an example of a class method I'm working with:
#staticmethod
def alpha_sampler(model):
# all the variables in this block are numpy arrays or floats
var_alpha = model.params.var_alpha
var_rating = model.params.var_rating
b = model.params.b
beta = model.params.beta
S = model.params.S
Z = model.params.Z
x_user_g0_inner_over_var = model.x_user_g0_inner_over_var
def _alpha_sampler(row):
feature_arr = row[2]
var_alpha_given_rest = 1/((1/var_alpha) + feature_arr.shape[0]*(1/var_rating))
i = row[0]
items = row[1]
O = row[3] - np.inner(feature_arr,b) - beta[items] - np.inner(S[i],Z[items])
E_alpha_given_rest = var_alpha_given_rest * (x_user_g0_inner_over_var[i] + O.sum()/var_rating)
return np.random.normal(E_alpha_given_rest,np.sqrt(var_alpha_given_rest))
return _alpha_sampler
As you can see, to avoid serialization errors, I define a static method that returns a function that is in turn applied to each row of an RDD (model is the parent class here, and this is called from within another method of model):
# self.grp_user is the RDD
self.params.alpha = np.array(self.grp_user.map(model.alpha_sampler(self)).collect())
Now, this all works fine, but is not leveraging Spark's broadcast variables at all. Ideally, all the variables I'm passing in this function (var_alpha, beta, S, etc.) could first be broadcast to the workers, so that I wasn't redundantly passing them as part of the map. But I'm not sure how to do this.
My question, then, is the following: How/where should I make these into broadcast variables such that they are available to the alpha_sampler function that I map to grp_user? One thing I believe will work would be to make them globals, e.g.
global var_alpha
var_alpha = sc.broadcast(model.params.var_alpha)
# and similarly for the other variables...
Then the alpha_sampler could be much simplified:
#staticmethod
def _alpha_sampler(row):
feature_arr = row[2]
var_alpha_given_rest = 1/((1/var_alpha.value) + feature_arr.shape[0]*(1/var_rating.value))
i = row[0]
items = row[1]
O = row[3] - np.inner(feature_arr,b.value) - beta.value[items] - np.inner(S.value[i],Z.value[items])
E_alpha_given_rest = var_alpha_given_rest * (x_user_g0_inner_over_var.value[i] + O.sum()/var_rating.value)
return np.random.normal(E_alpha_given_rest,np.sqrt(var_alpha_given_rest))
But of course this is really dangerous use of globals that I would like to avoid. Is there a better way that lets me leverage broadcast variables?

Assuming that variables you use here are simply scalars there is probably nothing to gain here from a performance perspective and using broadcast variables will make you code less readable but you can either pass a broadcast variable as an argument to the static method:
class model(object):
#staticmethod
def foobar(a_model, mu):
y = a_model.y
def _foobar(x):
return x - mu.value + y
return _foobar
def __init__(self, sc):
self.sc = sc
self.y = -1
self.rdd = self.sc.parallelize([1, 2, 3])
def get_mean(self):
return self.rdd.mean()
def run_foobar(self):
mu = self.sc.broadcast(self.get_mean())
self.data = self.rdd.map(model.foobar(self, mu))
or initialize it there:
class model(object):
#staticmethod
def foobar(a_model):
mu = a_model.sc.broadcast(a_model.get_mean())
y = a_model.y
def _foobar(x):
return x - mu.value + y
return _foobar
def __init__(self, sc):
self.sc = sc
self.y = -1
self.rdd = self.sc.parallelize([1, 2, 3])
def get_mean(self):
return self.rdd.mean()
def run_foobar(self):
self.data = self.rdd.map(model.foobar(self))

Printing from within properties

I'm trying to make a robotics kit. Its designed to be simple so I'm using properties so when the users change a parameter the property method sends the serial command which controls motors/ servos/whatever.
This is the code at the moment, directly from a previous question I asked on here.
class Servo(object):
def __init__(self, which_servo, angle = 0):
self._angle = angle;
self._servo_no = which_servo
def get_angle(self):
return self._angle
def set_angle(self, value):
self._angle = value
print "replace this print statement with the code to set servo, notice that this method knows the servo number AND the desired value"
def del_angle(self):
del self._angle
angle = property(get_angle, set_angle, del_angle, "I'm the 'angle' property.
this is then initialized as such:
class robot(object):
def __init___(self):
self.servos = [Servo(0), Servo(1), Servo(2), Servo(3)]
Now, this works in the respect that it does change the variable through the getter and setter functions, however the prints in the getter and setter never is printed, thus if I replace it with a serial command I assume it won't do anything either, can anyone shed any light on this?
Thanks
Update: Thanks for the help using the servo file this is whats happened, there are three scenarios the first works and by extension I would have assumed the next two preferable scenarios would work but they don't any ideas?
This works
import servo
class Robot(object):
def __init__(self):
self.servos = [servo.Servo(0, 0), servo.Servo(1,0), servo.Servo(2,0)]
R = Robot()
R.servos[1].angle = 25
This does not:
import servo
class Robot(object):
def __init__(self):
self.servos = [servo.Servo(0, 0), servo.Servo(1,0), servo.Servo(2,0)]
R = Robot()
left_servo = R.servos[1].angle
left_servo = 25
Neither does this
import servo
class Robot(object):
def __init__(self):
self.servos = [servo.Servo(0, 0).angle, servo.Servo(1,0).angle, servo.Servo(2,0).angle]
R = Robot()
R.servo[1] = 25

Using the preferred decorator syntax for properties, this works fine. It'll also help you avoid issues like this in the future
class Servo(object):
def __init__(self, which_servo, angle = 0):
self._angle = angle;
self._servo_no = which_servo
#property
def angle(self):
return self._angle
#angle.setter
def angle(self, value):
self._angle = value
print "replace this print statement with the code to set servo"
#angle.deleter
def angle(self):
del self._angle
Seeing as your indentation is off here, I believe this is likely an issue of indentation in your source. This should work as well if you really want to use the old property function:
class Servo(object):
def __init__(self, which_servo, angle = 0):
self._angle = angle;
self._servo_no = which_servo
def get_angle(self):
return self._angle
def set_angle(self, value):
self._angle = value
print "replace this print statement with the code to set servo"
def del_angle(self):
del self._angle
angle = property(get_angle, set_angle, del_angle,"I'm the 'angle' property.")
Both of these work successfully for me (inside a file called servo.py)
>>> import servo
>>> s = servo.Servo(1, 2)
>>> s.angle
2
>>> s.angle = 3
replace this print statement with the code to set servo
EDIT
To address your new issues. When you assign R.servos[1].angle to left_servo, its not creating a reference to the servos angle, it's just setting left_servo to whatever the angle is. When you reassign 25 to it, you're not assigning to the angle you're assigning to the left_servo.
On the second one, I'm assuming you meant R.servos and not R.servo which should be raising an AttributeError. But the real problem as I see it, is you should be saying R.servos[1].angle = 25 and you're omitting the .angle.
To (attempt to) put it simply: When you use the = operator, you are changing where a name refers to, not what it refers to.
>>> x = 1
>>> x = 2
the second assignment does not overwrite the 1 in memory with a 2, it just changes where x refers to. So if I did something like
>>> x = 1
>>> y = x
>>> y = 2
>>> print x
1
the output is 1 because your are telling y to refer to the same place that x refers. Changing y to 2 changes where y refers to, it does not change the 1 already in memory.