I am developing a game in Django in which the quantity of rebels updates after a turn change. Rebels are represented as integers from 0 to 100 in the (MySQL) database.
When I save, this happens:
print world.rebels
>>> 0
rebstab = 0
world.rebels += rebstab
world.save()
print world.rebels
>>> 0
However, when I use F() expressions (as I gather I should to prevent race conditions), this happens:
print world.rebels
>>> 0
rebstab = 0
world.rebels = F('rebels') + rebstab
world.save()
print world.rebels
>>> 100
What's going on?
I don't have any experience with using F() objects like this so this answer may not be useful, but having a look at the documentation it mentions:
In order to access the new value that has been saved in this way, the object will need to be reloaded:
reporter = Reporters.objects.get(pk=reporter.pk)
so you may have to actually query the DB again to see the updated value:
print world.rebels
>>> 0
rebstab = 0
world.rebels = F('rebels') + rebstab
world.save()
print World.objects.get(pk=world.pk)
>>> 100
Edit: Also look [at the example where you don't need to pull the objects into memory and can do everythign at the DB level:
World.objects.get(pk=...).update(rebels=F('rebels) + 1)
I just figured out the reason had nothing to do with the F() object itself but rather a conflict with a custom save method. See Django F() objects and custom saves weirdness for a more indepth explanation.
Related
I am using this code to create a solve a simple problem:
import pyomo.environ as pyo
from pyomo.core.expr.numeric_expr import LinearExpression
model = pyo.ConcreteModel()
model.nVars = pyo.Param(initialize=4)
model.N = pyo.RangeSet(model.nVars)
model.x = pyo.Var(model.N, within=pyo.Binary)
model.coefs = [1, 1, 3, 4]
model.linexp = LinearExpression(constant=0,
linear_coefs=model.coefs,
linear_vars=[model.x[i] for i in model.N])
def caprule(m):
return m.linexp <= 50
model.capme = pyo.Constraint(rule=caprule)
model.obj = pyo.Objective(expr = model.linexp, sense = maximize)
results = SolverFactory('glpk', executable='/usr/bin/glpsol').solve(model)
results.write()
And this is the output:
# ==========================================================
# = Solver Results =
# ==========================================================
# ----------------------------------------------------------
# Problem Information
# ----------------------------------------------------------
Problem:
- Name: unknown
Lower bound: 50.0
Upper bound: 50.0
Number of objectives: 1
Number of constraints: 2
Number of variables: 5
Number of nonzeros: 5
Sense: maximize
# ----------------------------------------------------------
# Solver Information
# ----------------------------------------------------------
Solver:
- Status: ok
Termination condition: optimal
Statistics:
Branch and bound:
Number of bounded subproblems: 0
Number of created subproblems: 0
Error rc: 0
Time: 0.09727835655212402
# ----------------------------------------------------------
# Solution Information
# ----------------------------------------------------------
Solution:
- number of solutions: 0
number of solutions displayed: 0
It says the number of solutions is 0, and yet it does solve the problem:
print(list(model.x[i]() for i in model.N))
Will output this:
[1.0, 1.0, 1.0, 1.0]
Which is a correct answer to the problem. what am I missing?
The interface between pyomo and glpk sometimes (always?) seems to return 0 for the number of solutions. I'm assuming there is some issue with the generalized interface between the pyomo core module and the various solvers that it interfaces with. When I use glpk and cbc solvers on this, it reports the number of solutions as zero. Perhaps those solvers don't fill that data element in the generalized interface. Somebody w/ more experience in the data glob returned from the solver may know precisely. That said, the main thing to look at is the termination condition, which I've found to be always accurate. It reports optimal.
I suspect that you have some mixed code from another model in your example. When I fix a typo or two (you missed the pyo prefix on a few things), it solves fine and gives the correct objective value as 9. I'm not sure where 50 came from in your output.
(slightly cleaned up) Code:
import pyomo.environ as pyo
from pyomo.core.expr.numeric_expr import LinearExpression
model = pyo.ConcreteModel()
model.nVars = pyo.Param(initialize=4)
model.N = pyo.RangeSet(model.nVars)
model.x = pyo.Var(model.N, within=pyo.Binary)
model.coefs = [1, 1, 3, 4]
model.linexp = LinearExpression(constant=0,
linear_coefs=model.coefs,
linear_vars=[model.x[i] for i in model.N])
def caprule(m):
return m.linexp <= 50
model.capme = pyo.Constraint(rule=caprule)
model.obj = pyo.Objective(expr = model.linexp, sense = pyo.maximize)
solver = pyo.SolverFactory('glpk') #, executable='/usr/bin/glpsol').solve(model)
results = solver.solve(model)
print(results)
model.obj.pprint()
model.obj.display()
Output:
Problem:
- Name: unknown
Lower bound: 9.0
Upper bound: 9.0
Number of objectives: 1
Number of constraints: 2
Number of variables: 5
Number of nonzeros: 5
Sense: maximize
Solver:
- Status: ok
Termination condition: optimal
Statistics:
Branch and bound:
Number of bounded subproblems: 0
Number of created subproblems: 0
Error rc: 0
Time: 0.00797891616821289
Solution:
- number of solutions: 0
number of solutions displayed: 0
obj : Size=1, Index=None, Active=True
Key : Active : Sense : Expression
None : True : maximize : x[1] + x[2] + 3*x[3] + 4*x[4]
obj : Size=1, Index=None, Active=True
Key : Active : Value
None : True : 9.0
I have seen this issue many times happening to many people (here). I am still struggling trying to validate whether what my dictionary captures from a JSON is "None" or not but I still get the following error.
This code is supposed to call a CURL looking for the 'closed' value in the 'status' key until it finds it (or 10 times). When payment is done by means of a QR code, status changes from opened to closed.
status = (my_dict['elements'][0]['status'])
TypeError: 'NoneType' object is not subscriptable
Any clue of what am I doing wrong and how can I fix it?
Also, if I run the part of the script that calls the JSON standalone, it executes smoothly everytime. Is it anything in the code that could be affecting the CURL execution?
By the way, I have started programming 1 week ago so please excuse me if I mix concepts or say something that lacks of common sense.
I have tried to validate the IF with "is not" instead of "!=" and also with "None" instead of "".
def show_qr():
reference_json = reference.replace(' ','%20') #replaces "space" with %20 for CURL assembly
url = "https://api.mercadopago.com/merchant_orders?external_reference=" + reference_json #CURL URL concatenate
headers = CaseInsensitiveDict()
headers["Authorization"] = "Bearer MY_TOKEN"
pygame.init()
ventana = pygame.display.set_mode(window_resolution,pygame.FULLSCREEN) #screen settings
producto = pygame.image.load("qrcode001.png") #Qr image load
producto = pygame.transform.scale(producto, [640,480]) #Qr size
trials = 0 #sets while loop variable start value
status = "undefined" #defines "status" variable
while status != "closed" and trials<10: #to repeat the loop until "status" value = "closed"
ventana.blit(producto, (448,192)) #QR code position setting
pygame.display.update() #
response = requests.request("GET", url, headers=headers) #makes CURL GET
lag = 0.5 #creates an incremental 0.5 seconds everytime return value is None
sleep(lag) #
json_data = (response.text) #Captures JSON response as text
my_dict = json.loads(json_data) #creates a dictionary with JSON data
if json_data != "": #Checks if json_data is None
status = (my_dict['elements'][0]['status']) #If json_data is not none, asigns 'status' key to "status" variable
else:
lag = lag + 0.5 #increments lag
trials = trials + 1 #increments loop variable
sleep (5) #time to avoid being banned from server.
print (trials)
From your original encountered error, it's not clear what the issue is. The problem is that basically any part of that statement can result in a TypeError being raised as the evaluated part is a None. For example, given my_dict['elements'][0]['status'] this can fail if my_dict is None, or also if my_dict['elements'] is None.
I would try inserting breakpoints to better assist with debugging the cause. another solution that might help would be to wrap each part of the statement in a try-catch block as below:
my_dict = None
try:
elements = my_dict['elements']
except TypeError as e:
print('It possible that my_dict maybe None.')
print('Error:', e)
else:
try:
ele = elements[0]
except TypeError as e:
print('It possible that elements maybe None.')
print('Error:', e)
else:
try:
status = ele['status']
except TypeError as e:
print('It possible that first element maybe None.')
print('Error:', e)
else:
print('Got the status successfully:', status)
I'm just starting to learn how to code in Sagemath, I know it's similar to python but I don't have much experience with that either.
I'm trying to add two binary numbers representing fractions. That is, something like
a = '110'
b = '011'
bin(int(a,2) + int(b,2))
But using values representing fractions, such as '1.1'.
Thanks in advance!
If you want to do this in vanilla Python, parsing the binary fractions by hand isn't too bad (the first part being from this answer);
def binstr_to_float(s):
t = s.split('.')
return int(t[0], 2) + int(t[1], 2) / 2.**len(t[1])
def float_to_binstr(f):
i = 0
while int(f) != f:
f *= 2
i += 1
as_str = str(bin(int(f)))
if i == 0:
return as_str[2:]
return as_str[2:-i] + '.' + as_str[-i:]
float_to_binstr(parse_bin('11.1') + parse_bin('0.111')) # is '100.011'
In python you can use the Binary fractions package. With this package you can convert binary-fraction strings into floats and vice-versa. Then, you can perform operations on them.
Example:
>>> from binary_fractions import Binary
>>> sum = Binary("1.1") + Binary("10.01")
>>> str(sum)
'0b11.11'
>>> float(sum)
3.75
>>>
It has many more helper functions to manipulate binary strings such as: shift, add, fill, to_exponential, invert...
PS: Shameless plug, I'm the author of this package.
ok I am trying to create a definition which will read a list of IDS from an external Json file, Which it is doing. Its even putting the data into the database on load of the program, my issue is this. I cant seem to match the list IDs to a comparison. Here is my current code:
def check(account):
global ID_account
import json, httplib
if not hasattr(BigWorld, 'iddata'):
UID_DB = account['databaseID']
UID = ID_account
try:
conn = httplib.HTTPConnection('URL')
conn.request('GET', '/ids.json')
conn.sock.settimeout(2)
resp = conn.getresponse()
qresp = resp.read()
BigWorld.iddata = json.loads(qresp)
LOG_NOTE('[ABRO] Request of URL data successful.')
conn.close()
except:
LOG_NOTE('[ABRO] Http request to URL problem. Loading local data.')
if UID_DB is not None:
list = BigWorld.iddata["ids"]
#print (len(list) - 1)
for n in range(0, (len(list) - 1)):
#print UID_DB
#print list[n]
if UID_DB == list[n]:
#print '[ABRO] userid located:'
#print UID_DB
UID = UID_DB
else:
LOG_NOTE('[ABRO] userid not set.')
if 'databaseID' in account and account['databaseID'] != UID:
print '[ABRO] Account not active in database, game closing...... '
BigWorld.quit()
now my json file looks like this:
{
"ids":[
"1001583757",
"500687699",
"000000000"
]
}
now when I run this with all the commented out prints it seems to execute perfectly fine up till it tries to do the match inside the for loop. Even when the print shows UID_DB and list[n] being the same values, it does not set my variable, it doesn't post any errors, its just simply acting as if there was no match. am I possibly missing a loop break? here is the python log starting with the print of the length of the table print:
INFO: 2
INFO: 1001583757
INFO: 1001583757
INFO: 1001583757
INFO: 500687699
INFO: [ABRO] Account not active, game closing......
as you can see from the log, its never printing the User located print, so it is not matching them. its just continuing with the loop and using the default ID I defined above the definition. Anyone with an idea would definitely help me out as ive been poking and prodding this thing for 3 days now.
the answer to this was found by #VikasNehaOjha it was missing simply a conversion to match types before the match comparison I did this by adding in
list[n] = int(list[n])
that resolved my issue and it finally matched comparisons.
Many random-number generators return floating numbers between 0 and 1.
What's the best and correct way to get integers between a and b?
Divide the interval [0,1] in B-A+1 bins
Example A=2, B=5
[----+----+----+----]
0 1/4 1/2 3/4 1
Maps to 2 3 4 5
The problem with the formula
Int (Rnd() * (B-A+1)) + A
is that your Rnd() generation interval is closed on both sides, thus the 0 and the 1 are both possible outputs and the formula gives 6 when the Rnd() is exactly 1.
In a real random distribution (not pseudo), the 1 has probability zero. I think it is safe enough to program something like:
r=Rnd()
if r equal 1
MyInt = B
else
MyInt = Int(r * (B-A+1)) + A
endif
Edit
Just a quick test in Mathematica:
Define our function:
f[a_, b_] := If[(r = RandomReal[]) == 1, b, IntegerPart[r (b - a + 1)] + a]
Build a table with 3 10^5 numbers in [1,100]:
table = SortBy[Tally[Table[f[1, 100], {300000}]], First]
Check minimum and maximum:
In[137]:= {Max[First /# table], Min[First /# table]}
Out[137]= {100, 1}
Lets see the distribution:
BarChart[Last /# SortBy[Tally[Table[f[1, 100], {300000}]], First],
ChartStyle -> "DarkRainbow"]
X = (Rand() * (B - A)) + A
Another way to look at it, where r is your random number in the range 0 to 1:
(1-r)a + rb
As for your additional requirement of the result being an integer, maybe (apart from using built in casting) the modulus operator can help you out. Check out this question and the answer:
Expand a random range from 1–5 to 1–7
Well, why not just look at how Python does it itself? Read random.py in your installation's lib directory.
After gutting it to only support the behavior of random.randint() (which is what you want) and removing all error checks for non-integer or out-of-bounds arguments, you get:
import random
def randint(start, stop):
width = stop+1 - start
return start + int(random.random()*width)
Testing:
>>> l = []
>>> for i in range(2000000):
... l.append(randint(3,6))
...
>>> l.count(3)
499593
>>> l.count(4)
499359
>>> l.count(5)
501432
>>> l.count(6)
499616
>>>
Assuming r_a_b is the desired random number between a and b and r_0_1 is a random number between 0 and 1 the following should work just fine:
r_a_b = (r_0_1 * (b-a)) + a