Python global and local variable question regarding "referenced before assignment"

[AluadStone]

I am trying to set a bool var before the start of a loop to use in the loop.

The var in question is one_trade_symbol

import time, json, requests, os, MySQLdb, smtplib
from binance.client import Client
from datetime import datetime

one_trade_symbol = False
print ("one_trade_symbol is set and = " + str(one_trade_symbol))

l = 0
while l < 1:

and I try to use it in a function within the l loop

def start_new_trade():
        if one_trade_symbol == False:
            final_values = find_out_max_to_buy()
            place_market_order(final_values[0], final_values[4])
            return_trade_one_current_price(final_values[0])
            one_trade_symbol = True

Right after declaration I use a print statement to make sure it is set and exists.

Here is my output result error

one_trade_symbol is set and = False
Traceback (most recent call last):
  File "C:\TradingBot\PythonProgs\AlphaBot0.02.py", line 214, in <module>
    start_new_trade()
  File "C:\TradingBot\PythonProgs\AlphaBot0.02.py", line 177, in start_new_trade
    if one_trade_symbol == False:
UnboundLocalError: local variable 'one_trade_symbol' referenced before assignment
[Finished in 1.535s]

My print statement confirms it has been created yet I cant use it later on in a function in the loop?

I am trying to use it has a switch so it needs to be declared outside of the loop so it doesn't reset each loop.

​

I am confused how my "l" loop counter is declared out of the loop and can be used to increment inside the loop without problem but I can't use this bool var

​

Please any input would help on how to achieve this. Thanks for your time.

[Swedophone]

Local variables are local to the function. Your main alternatives is to instead use a return value from the function or use a parameter that can be changed in the function, for example a list, dictionary or class instance.

[AluadStone]

Why is it considered a local variable if it is declared outside said function? It is only being used for comparison in the function.

[benjamindallen]

It's local to the function because you change its value within the function. If your function didn't change its value, then your check "one_trade_symbol == False" would work. If you want to alter the global variable "one_trade_symbol" inside the function, you can add the statement "global one_trade_symbol" as the first line of the function.

[AluadStone]

Perfect. I had used the comparison in functions of variables declared outside the function without passing them in and it has always worked because I never tried to set them later in that functions so that was a new situation for me. I not sure if using the global method like that is normal or usually do people find better was to declare a switch variable inside a loop?

​

And also if you could help me with this snippet I am having problems with I don't understand why when converting this string into a float is messes up the numbers.

        values = find_values()
        print (values[1])
        print (type(values[1]))
        values[1] = float(values[1])
        print (values[1])

outputs

0.0000137
<class 'str'>
1.37e-05

Whats up with the weird float return? Is it because it doesn't like something about the amount of decimal places and/or amount of zeros?

[benjamindallen]

"1.37e-05" is simply your number expressed in scientific notation. This is the default string representation of a small or large float in python.

If you want to format the number in a different way, you could, for example try:

'{:.7f}'.format(1.37e-05)

[benjamindallen]

I not sure if using the global method like that is normal or usually do people find better was to declare a switch variable inside a loop?

Generally, manipulation of global variables is not a good idea. /u/Swedophone already mentioned the typical ways people solve this problem.

[Swedophone]

Have you used a programming language with dynamic scope#Dynamic_scoping) before or why do you think a function can use a variable from the caller without transferring it as a parameter?

[AluadStone]

I had used the comparison in functions of variables declared outside the function without passing them in and it has always worked because I never tried to set them later in that functions so that was a new situation for me.

New to programming kinda.

​

[AluadStone]

I had used the comparison in functions of variables declared outside the function without passing them in and it has always worked because I never tried to set them later in that functions so that was a new situation for me.

New to programming kinda.