When function calls global variables, a lot a CPU cycles is consumed.

Noncompliant Code Example

global_var = 'foo'
def print_global_var_details():
    print(len(global_var)) # Noncompliant
    print('Global var : ', global_var) # Noncompliant
    print('Global var : ' + global_var) # Noncompliant
print_global_var_details()

Compliant Solution

global_var = 'foo';
def print_var_details(local_var) {
    print(len(local_var));
    print('Var : ', local_var)
    print('Var : ' + local_var)
}
print_length(global_var);