Getting an updated object value inside a Python for loop-CodePudding

I have an object called "ticker" that is collecting streaming data from Interactive Brokers via ib_insync.

I am simply trying to create a list and updated it with new, for example, bid prices from the ticker object every 250 milliseconds or so. When I try to get updated values via the for loop, I am not getting updated values through each iteration, just the original value from the first pass.

I assume I have a lack of understanding around scope inside the for loop which is creating this issue. How can I do this correctly?

Here is the code:

contract = Stock('IBM', 'SMART', 'USD') # this defines the contract
ticker = ib.reqMktData(contract) # this creates the ticker object for the specified contract
vec = [0] * 100
for m in vec:
    vec.pop(0)
    vec.append(ticker.bid)
    print(vec)
    time.sleep(.25)

CodePudding user response：

Need to make a copy of vec and alter the copy in the for loop wih <copy>.append.

ie if you have loop

for i in something: then something must not be changed inside the loop.

CodePudding user response：

In Python you can not change the object you loop over. But given the description of your goal we can work around that. Either update your list a fixed number of times (n_iter) like that:

for _ in range(n_iter):
    vec = vec[:-1]   [ticker.bid]
    print(ticker.bid)
    time.sleep(0.25)

Or use a function that returns True if the updating should continue and False if it should stop like that:

while should_proceed():
    vec = vec[:-1]   [ticker.bid]
    print(ticker.bid)
    time.sleep(0.25)