I am trying to follow syntax of the pyparticleio.ParticleCloud package. Using the following command, my code works correctly "particle_cloud.boron1.led('on')" (hardcoded values)
I want to pass portions of the command, "boron1" and "on" as variable. I'm trying to figure out how to use those variables to act in the same way as if i'd hardcoded the values.
My python level is very beginner.
command_list['boron1','on']
device = command_list[0]
function_1 = command_list[1]
access_token = "ak3bidl3xxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
particle_cloud = ParticleCloud(username_or_access_token=access_token)
#particle_cloud.boron1.led('on') #hardcoded example that works
particle_cloud.device.led(function_1) #what i would like to work
If you set device to the actual object, you can call methods on the object. Example:
device = particle_cloud.boron1 # Or whatever you like
arg = 'on' # Also make this whatever you like
device.led(arg) # Same as: particle_cloud.boron1.led('on')
Python has a built in function called exec
It allows you to take a string, and have Python execute it as code.
A basic example based on the code you provided would look like this:
command_list['boron1','on']
device = command_list[0]
function_1 = command_list[1]
exec('particle_cloud.' + device + '.led("' + function_1 + '")')
This is a bit ugly, but there are different ways to compose strings in Python such as using join or format so depending on your real code you may be able to build something nice.
Just be careful not to pass raw user input to exec!
I can cause all kinds of trouble from errors to security issues.
I believe you could use getattr() (in Python3: https://docs.python.org/3/library/functions.html#getattr ) :
pcdevice = getattr(particle_cloud, device)
pcdevice.led(function_1)
(BTW, I woudln't name the string 'on' with the label 'function_1' as the variable name implies that this option is a function when it is a string. Also, the above may now work depending on the properties of your library object ParticleCloud.)
Related
I am using pywin32 to automate some tasks in software that has an Automation Server technology interface (formerly OLE Automation Server).
This software comes with a somewhat detailed manual with code examples in VBA, C++ or Matlab but no Python. I have built a Python library that can do most of the functionalities built into the software but there are some parts I cannot do in Python.
I cannot change the value of a property if this property is contained in a iterable COM object.
What I can do:
[Documentation for Visibility property]
import win32com.client
app = win32com.client.Dispatch('NAME_OF_APP')
app.Visibility = True
As an example, with this code, I can change the visibility parameter of the software: if it runs with or without GUI.
What I cannot do:
[Documentation for getting and setting current device]
import win32com.client
app = win32com.client.Dispatch('NAME_OF_APP')
app.CurrentDevice(0) = 'NAME OF DEVICE'
I then get the following error:
SyntaxError: cannot assign to function call here. Maybe you meant '==' instead of '='?
This error makes sense to me but I cannot find a way to set any of these software properties when they come in the form of an iterable object. As soon as I have to specify an index, I don't know how to set the value.
From what I understand, in C++ we are able to change the value because of pointers but how can we achieve the same thing in Python? Is it possible or do I have to use some C++ code in parallel to my Python to run my library? I don't know anything in C++ so if I could avoid doing that, it would be good.
What I have tried
Of course, the 1st thing I tried was to change () to [] or {} which logically didn't work.
Then I used the Evaluate function in PyCharms to see what was hiding behind my app.CurrentDevice. I was hoping to find sub-attributes that I could then set but I don't see anything inside the object:
[Result of Evaluate on the CurrentDevice object]
Finally, I have tried the following:
import win32com.client
app = win32com.client.Dispatch('NAME_OF_APP')
curr_device = app.CurrentDevice(0)
curr_device = 'NAME OF DEVICE'
I wanted to affect the object to a variable and then change the value but of course, this only rewrites the variable curr-device with 'NAME OF DEVICE' but loses any link to COM Object.
I feel like my questions are similar to the following unanswered question:
How can I set the value of an indexed property of a COM object in Python?
It looks as if win32com is struggling to set the property if there is an additional argument to the put function, which is a little surprising.
First thing to do is to use
app = win32com.client.gencache.EnsureDispatch('NAME_OF_APP')
This creates a Python wrapper for the COM object (rather than just firing function calls at the object and hoping). This may in itself clear up your issue.
If not, here is a quite ugly way of working around. As you have identified, the relevant part of the type library is:
[id(0x00000018),propput, helpstring("property CurrentDevice")]
HRESULT CurrentDevice([in] long lAcq, [in] VARIANT pVal);
And you can use this to set the property at a low level.
win32com dispatch objects are a wrapper for the PyIDispatch object. All dispatch objects support the Invoke method, and you can use this to call the function yourself. NB. Since I don't have access to your COM object, I can't test, so this answer may need some tweaking (!).
The PyIDispatch documentation
Try:
import win32com.client as wc
import pythoncom
app = wc.gencache.EnsureDispatch('NAME OF APP')
app.Visibility=TRUE
newVal = wc.VARIANT(pythoncom.VT_VARIANT,'NAME OF DEVICE')
app._oleobj_.Invoke(24,0,pythoncom.INVOKE_PROPERTYPUT,0,0,newVal)
There are a lot of 'magic' numbers here, but basically:
24 = 0x00000018 in decimal: this is the Id of the property
0 = the LCID, the Locale Id ... I always set it to 0
pythoncom.INVOKE_PROPERTYPUT = the type of call.
0 = whether you care about the return type (you probably don't = False)
0 = first parameter, lAcq, as in CurrentDevice(0)
newVal = second paramter,pVal, the new device name as a VARIANT
I haven't tried this, but pythoncom is pretty good about converting VARIANT types, so you might not need the VARIANT creation, and can just use NAME OF DEVICE directly as the parameter.
I am working on a machine learning modelling problem where an object is created to store training and validation data, but the validation set if optional and if not included when creating the object the default value is None.
If we find out later on though the user wants to add a validation pandas dataframe we were hoping to let them supply the name of the dataframe with input(). With a function defined right in the notebook we're running we can then do an eval(<input>) to turn the string into the object we need. If we define the object outside of our notebook though it seems like the scope doesn't include that variable.
I realize this probably isn't the best way to do this, so what is a more pythonic way to let a user supply a dataframe by name after an object as already been instantiated? We can pass the objects fine as arguments to functions. Is there a way to pass an object like that but with input() or some other user-friendly way to prompt the user?
It maybe possible to use locals() or globals() as a dict for grabbing an initialized variable by it's name.
the_variable = {'key_one': 'val_one'}
selected_input = input("Please input a variable name")
selected_var = locals()[selected_input]
print("selected_var continence -> {0}".format(selected_var))
Should output, well assuming the_variable was passed to input()
selected_var continence -> {'key_one': 'val_one'}
This is an adaptation of an answer to Calling a function of a module by using it's name a string, but seems to work in this instance too.
Update
I can't remember where I picked up the following perversion (I did look about though), and I'm not suggesting it's use in production. But...
questionable_response = lambda message: input("{message}: ".format(message = message))
this_response = json.loads(questionable_response("Input some JSON please"))
# <- '{"Bill": {"person": true}, "Ted": {"person": "Who is asking?"}}'
... does allow for object like inputting.
And getting data from an inputted json string could look like...
this_response['Bill']
# -> {u'person': True}
this_response['Ted'].get('person')
# -> u'Who is asking?'
... however, you'll likely see some issues with using above with other scripted components.
For the Unicode conversion there's some pre-posted answers on the subject. And checking help(json.loads) exposes that there's toggles for parse_ing floats, ints, and constants.
Even with that it may not be worth it, because there's still some oddities you'll run into if trying to implement this funkiness.
Just to list a few;
conjunctions are a no go; let's say ya get a clever Clara who inputs something like '{"Clara": {"person": "I'll not be labelled!"}}'. That would cause an error unless ' was escaped, eg. \'
the above is also quote fragile; perhaps someone at the keyboard hasn't had enough to drink and tries "{'Jain': {'person': True}}". That would first barf on quotes, then heave from True not being true
So like I prefaced at the start of this update, I'll not recommend this in production; could waist a lot of time chasing edge-cases. I only share it because maybe you've not found any other option for getting from input to something that can be interrogated like an object.
I would like to use a function's parameter to create dynamic names of dataframes and/or objects in Python. I have about 40 different names so it would be really elegant to do this in a function. Is there a way to do this or do I need to do this via 'dict'? I read that 'exec' is dangerous (not that I could get this to work). SAS has this feature for their macros which is where I am coming from. Here is an example of what I am trying to do (using '#' for illustrative purposes):
def TrainModels (mtype):
model_#mtype = ExtraTreesClassifier()
model_#mtype.fit(X_#mtype, Y_#mtype)
TrainModels ('FirstModel')
TrainModels ('SecondModel')
You could use a dictionary for this:
models = {}
def TrainModels (mtype):
models[mtype] = ExtraTreesClassifier()
models[mtype].fit()
First of all, any name you define within your TrainModels function will be local to that function, so won't be accessible in the rest of your program. So you have to define a global name.
Everything in Python is a dictionary, including the global namespace. You can define a new global name dynamically as follows:
my_name = 'foo'
globals()[my_name] = 'bar'
This is terrible and you should never do it. It adds too much indirection to your code. When someone else (or yourself in 3 months when the code is no longer fresh in your mind) reads the code and see 'foo' used elsewhere, they'll have a hard time figuring out where it came from. Code analysis tools will not be able to help you.
I would use a dict as Milkboat suggested.
Forgive this rather basic Python question, but I literally have very little Python experience. I'm create a basic Python script for use with Kodi:
http://kodi.wiki/view/List_of_built-in_functions
Example code:
import kodi
variable = "The value to use in PlayMedia"
kodi.executebuiltin("PlayMedia(variable)")
kodi.executebuiltin("PlayerControl(RepeatAll)")
Rather than directly providing a string value for the function PlayMedia, I want to pass a variable as the value instead. The idea is another process may modify the variable value with sed so it can't be static.
Really simple, but can someone point me in the right direction?
It's simple case of string formatting.
template = "{}({})"
functionName = "function" # e.g. input from user
arg = "arg" # e.g. input from user
formatted = template.format(functionName, arg)
assert formatted == "function(arg)"
kodi.executebuiltin(formatted)
OK as far as I get your problem you need to define a variable whose value could be changed later, so the first part is easier, defining a variable in python is as simple as new_song = "tiffny_avlord_I_love_u", similarly you can define another string as new_video = "Bohemia_on_my_feet", the thing to keep in mind is that while defining variables as strings, you need to encapsulate all the string inside the double quotes "..." (However, single quotes also work fine)
Now the issue is how to update it's value , the easiest way is to take input from the user itself which can be done using raw_input() as :
new_song = raw_input("Please enter name of a valid song: ")
print "The new song is : "+new_song
Now whatever the user enters on the console would be stored in the variable new_song and you could use this variable and pass it to any function as
some_function(new_song)
Try executing this line and you will understand how it works.
I am writing some program using python and the z3py module.
What I am trying to do is the following: I extract a constraint of an if or a while statement from a function which is located in some other file. Additionally I extract the used variables in the statement as well as their types.
As I do not want to parse the constraint by hand into a z3py friendly form, I tried to use evaluate to do this for me. Therefore I used the tip of the following page: Z3 with string expressions
Now the problem is: I do not know how the variables in the constraint are called. But it seems as I have to name the handle of each variable like the actual variable. Otherwise evaluate won't find it. My code looks like this:
solver = Solver()
# Look up the constraint:
branch = bd.getBranchNum(0)
constr = branch.code
# Create handle for each variable, depending on its type:
for k in mapper.getVariables():
var = mapper.getVariables()[k]
if k in constr:
if var.type == "intNum":
Int(k)
else:
Real(k)
# Evaluate constraint, insert the result and solve it:
f = eval(constr)
solver.insert(f)
solve(f)
As you can see I saved the variables and constraints in classes. When executing this code I get the following error:
NameError: name 'real_x' is not defined
If I do not use the looping over the variables, but instead the following code, everything works fine:
solver = Solver()
branch = bd.getBranchNum(0)
constr = branch.code
print(constr)
real_x = Real('real_x')
int_y = Int('int_y')
f = eval(constr)
print(f)
solver.insert(f)
solve(f)
The problem is: I do not know, that the variables are called "real_x" or "int_y". Furthermore I do not know how many variables there are used, which means I have to use some dynamic thing like a loop.
Now my question is: Is there a way around this? What can I do to tell python that the handles already exist, but have a different name? Or is my approach completely wrong and I have to do something totally different?
This kind of thing is almost always a bad idea (see Why eval/exec is bad for more details), but "almost always" isn't "always", and it looks like you're using a library that was specifically designed to be used this way, in which case you've found one of the exceptions.
And at first glance, it seems like you've also hit one of the rare exceptions to the Keep data out of your variable names guideline (also see Why you don't want to dynamically create variables). But you haven't.
The only reason you need these variables like real_x to exist is so that eval can see them, right? But the eval function already knows how to look for variables in a dictionary instead of in your global namespace. And it looks like what you're getting back from mapper.getVariables() is a dictionary.
So, skip that whole messy loop, and just do this:
variables = mapper.getVariables()
f = eval(constr, globals=variables)
(In earlier versions of Python, globals is a positional-only argument, so just drop the globals= if you get an error about that.)
As the documentation explains, this gives the eval function access to your actual variables, plus the ones the mapper wants to generate, and it can do all kinds of unsafe things. If you want to prevent unsafe things, do this:
variables = dict(mapper.getVariables())
variables['__builtins__'] = {}
f = eval(constr, globals=variables)