I am using Python/Gurobi to optimize a problem. I generated variables using GRBaddVar through this code:
x[1,i,j,t] = model.addVar(vtype="B", name="x(1,%s,%s,%s)" % (i,j,t))
I also want to remove some variables in order to save some space. The variable is removed when a certain condition is true. Suppose the condition is when R = 1. To remove the variable I use the following code.
if R == 1:
x[1,i,j,t] = model.delVars(vtype="B", name="x(1,%s,%s,%s)" % (i,j,t))
However, it resulted in the following error:
AttributeError: 'gurobipy.Model' object has no attribute 'delVars'
I have no idea what's wrong with the code since I just follow the documentation (attached below) from Gurobi. Thanks for your help!
As David noted, you are looking at the documentation for the C API.
In the Python API, you can remove a single variable with the Model.remove() method, using the Var object the argument. E.g.,
model.remove(x[1,i,j,t])
You can use this same method to remove, e.g., a list of Var objects at once.
Note that you should call Model.update() before removing variables in this manner.
"You can use this same method to remove, e.g., a list of Var objects at once."
Can anyone suggest how to remove multiple variables at once. I have the variable to be removed in a dict/list format. I am trying to the below code, but error appears: GurobiError: Item to be removed not a Var, MVar, Constr, MConstr, SOS, QConstr, or GenConstr
model.remove(var_to_remove_dict.keys())
Related
I've created a function which can take a parameter which defines another call to manipulate a list. For example if I call sliprotor(Rotorid1, 1) directly, then the Rotorid1 list is manipulated as I want. Function below:
def sliprotor(rotorid,offset_qty):
for movers in range(26,0,-1):
rotorid[movers-1+offset_qty]=rotorid[movers-1]
for movers_refill in range(offset_qty):
rotorid[movers_refill]=rotorid[movers_refill+26]
However, if I try to call this 'indirectly' by building the list name and then executing it, 'rotorid' is not translated to the value, as it is when called directly.
The way I am doing this is
def set_curr_rotor(XX):
rotorid = "Rotorid"+str(XX)
return rotorid
rid1 = input("First rotor slip : ")
if(rid1):
sliprotor(set_curr_rotor(rid1),1)
So the 'indirect' call doesn't pass the value created by the set_curr_rotor function into the sliprotor function. The direct call does use the passed in value.
If I look in debug, you can see that it is directly calling rotorid[] as the list, not Rotorid1 or other Rotoridx and hence I get an index error.
....
File "", line 3, in sliprotor
rotorid[movers-1+offset_qty]=rotorid[movers-1]
IndexError: string index out of range
I could restructure the way I have the code, but I would prefer not to. Is there some method / scope issue I am missing? Is this just an intrinsic attribute of Python? I'm very new to Python so I'm just doing an exercise to model an Enigma machine.
Any help appreciated.
Ed
I'll assume that you have defined your rotors already, something like this:
Rotorid1 = list('abcdefghijklmnopqrstuvwxyz')
Rotorid2 = list('abcdefghijklmnopqrstuvwxyz')
And now you're reluctant to change this, because ... reasons.
That's fine. But you're still wrong. What you need to do is to create a larger data structure. You can do it like this:
Rotors = [ Rotorid1, Rotorid2, ... ]
Now you have a list-of-lists. The Rotors variable now contains all the various Rotorid variables. (Well, it references them. But that'll do.)
Instead of passing in the variable name as a handle to the rotor, you can simply pass in an index number:
def set_rotor(id):
global Current_rotor
Current_rotor = id
def slip_rotor(amount):
global Current_rotor
global Rotors
rotor = Rotors[Current_rotor]
for movers in range(26,0,-1):
rotor[movers-1+offset_qty]=rotor[movers-1]
# etc...
Also, be sure an look up slicings in Python - you can do a lot by manipulating sublists and substrings using slices.
I am new on chemical network model. Currently I am converting a previous student python code to adapt the new version in the lab as titled.
firstly, a gas mixture from mechanism (pre defined) is defined
gas_mix = ct.import_phases(mech,['gas'])
then, I want to get the number of the species and use cantera nSpecies
nsp = gas_mix.nSpecies()
and I got the error message as
AttributeError: 'list' object has no attribute 'nSpecies'
Also I tried:
nsp = gas_mix.n_species
and it also shows
AttributeError: 'list' object has no attribute
Would you please kindly help me on this ?
Thank you and best regards,
YouBe
It looks like import_phases returns a list of objects--either a list of "gas mix" or just "gas" objects. I'm not really sure because this is very specific to the program you're working with.
Anyway, try looping over the values in the gas_mix and see if you can call the nSpecies() method or access the n_species attribute:
gas_mix = ct.import_phases(mech,['gas'])
for gm in gas_mix:
print(gm.nSpecies())
# or you can try this:
print(gm.n_species)
Maybe that will get you closer to what you want.
The function import_phases returns a list, which is useful for the case where you want to import multiple phase definitions from the same file, e.g.
mixtures = ct.import_phases(mech, ['gas1', 'gas2'])
where both mixtures[0] and mixtures[2] will then be a single phase definition. If you only want to define a single phase, it is easier to write:
gas_mix = ct.Solution(mech,'gas')
Or, if the mechanism file only contains one phase definition, just
gas_mix = ct.Solution(mech)
From here, you should be able to access the number of species as
gas_mix.n_species
Many of the details of migrating from the old to new Cantera interfaces are described in the documentation page "Migrating from the Old Python Module".
I have a whole series of arrays with similar names mcmcdata.rho0, mcmcdata.rho1, ... and I want to be able to loop through them while updating their values. I can't figure out how this might be done or even what such a thing might be called.
I read my data in from file like this:
names1='l b rho0 rho1 rho2 rho3 rho4 rho5 rho6 rho7 rho8 rho9 rho10 rho11 rho12 rho13 rho14 rho15 rho16 rho17 rho18 rho19 rho20 rho21 rho22 rho23'.split()
mcmcdata=np.genfromtxt(filename,names=names1,dtype=None).view(np.recarray)
and I want to update the "rho" arrays later on after I do some calculations.
for jj in range(dbins):
mcmc_x, mcmc_y, mcmc_z = wf.lbd_to_xyz(mcmcdata.l,mcmcdata.b,d[jj],R_sun)
rho, thindisk, thickdisk, halo = wf.total_density_fithRthinhRthickhzthinhzthickhrfRiA( mcmc_x, mcmc_y, mcmc_z, R_sun,params)
eval("mcmcdata."+names1[2+jj]) = copy.deepcopy(rho)
eval("mcmcthin."+names1[2+jj]) = copy.deepcopy(thindisk)
eval("mcmcthick."+names1[2+jj]) = copy.deepcopy(thickdisk)
eval("mcmchalo."+names1[2+jj]) = copy.deepcopy(halo)
But the eval command is giving an error:
File "<ipython-input-133-30322c5e633d>", line 13
eval("mcmcdata."+names1[2+jj]) = copy.deepcopy(rho)
SyntaxError: can't assign to function call
How can I loop through my existing arrays and update their values?
or
How can identify the arrays by name so I can update them?
The eval command doesn't work the way you seem to think it does. You appear to be using it like a text-replacement macro, hoping that Python will read the given string and then pretend you wrote that text in the original source code. Instead, it receives a string, and then it executes that code. You're giving it an expression that refers to an attribute of an object, which is fine, but the result of evaluating that expression does not yield a thing you can assign to. It yields the value of that attribute.
Although Python provides eval, it also provides many other things that often obviate the need for eval. In the case of your code, Python provides setattr. You give it an object, the name of an attribute on that object, and a value, and it assigns that object's attribute to refer to the given value.
setattr(mcmcdata, names1[2+jj], copy.deepcopy(rho))
It might make the code more readable to get rid of the names1 portion, too. I might write the code like this:
setattr(mcmcdata, 'rho' + str(jj), copy.deepcopy(rho))
That way, it's clear that I'm assigning the rho-related attributes of the object without having to go look at what's held in the names1 list; the name names1 doesn't offer much information about what's in it.
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)
I think this is probably something really simple, but I'd appreciate a hint:
I am using a python list to hold some some database insert statements:
list = [ "table_to_insert_to" ],["column1","column2"],[getValue.value1],["value2"]]
The problem is one of the values isn't evaluated until runtime-- so before the page even gets run, it breaks when it tries to import the function.
How do you handle this?
You've just pointed out one (out of a zillion) problems with global variables: not using global variables is the best solution to this problem and many others. If you still mistakenly believe you must use a global variable, put a placeholder (e.g. None) in the place where the value you don't yet know will go, and assign the right value there when it's finally known.
Just wrap it in a function and call the function when you have the data to initialize it.
# module.py
def setstatement(value1):
global sql
sql = ['select', 'column1', 'column2', value1]
# some other file
import module
module.setstatement(1)
# now you can use it.
>>> module.sql
['select', 'column1', 'column2', 1]
May be put functions instead of value, these functions should be called at run time and will give correct results e.g.
def getValue1Func():
return getValue.value1
my_list = [ "table_to_insert_to" ],["column1","column2"],[getValue1Func],["value2"]]
now I do not know how you use this list(I think there will be better alternatives if you state the whole problem), so while using list just check if value is callable and call it to get value
e.g.
if isinstance(val, collections.Callable):
val = val()
edit: for python < 2.6, you should use operator.isCallable