It may seem a silly question: How deep in the loops and conditionals a global variable is used?
I have the following piece of code (the full code is provided at the end):
blockchain = []
index_ul = 0
...
def print_blockchain_elements():
for block in blockchain:
print('Outputting block:')
print(block)
if block == blockchain[index_ul]:
print("block matches!")
index_ul += 1
while True:
print("Please choose: ")
print("Press 1 for: Add a new transaction value")
print("Press 2 for: Outputting the blockchain blocks")
user_choice = get_user_choice()
if user_choice == "1":
tx_amount = get_transaction_value()
add_value(tx_amount, get_last_blockchain_item())
else:
print_blockchain_elements()
When I run the code and the if statement if block == blockchain[index_ul]: is hit, i got the following error message:
Traceback (most recent call last):
File "/home/v/blc.py", line 67, in <module>
print_blockchain_elements()
File "/home/v/blc.py", line 48, in print_blockchain_elements
if block == blockchain[index_ul]:
UnboundLocalError: local variable 'index_ul' referenced before assignment
Now, i work in Visual Studio Code. when writing index_ul at blockchain[index_ul], VSC provides me hints for autocomplete, as it sees the variable.
Why I get this local variable error when the variable is defined globally?
The rest of the code (I know that I have an endless while loop):
#!/usr/bin/env python3.7
# Initializing our blockchain list
blockchain = []
# This index value is used in the if statement in order to test correct functioning of the "for" loop when parsing list items
index_ul = 0
# The following declared function returns the value of the last positional element of the blockchain list
def get_last_blockchain_item():
""" It returns the last value of the current blockchain"""
return blockchain[-1] #the -1 is the first negative positional index, meaning, the last item in a list
# This function accepts 2 arguments.
# One of the arguments is required when calling the function (transaction_amount);
# Another one is an optional argument when calling the function (last_transaction);
# The optional argument is optional because it is a default argument, meaning that has its value defined when the function is declared
def add_value(transaction_amount, last_transaction=[1]):
""" Append a new value as well as the last blockchain value to the blockchain
Arguments:
:transaction_amount: The amount that should be added.
:last_transaction: The last blockchain transaction (default [1])
"""
# This code calls a method (.append) on an existing global variable of type string
# append() method adds a value at the end of the list
# In this case the added value is a list, marked with []
blockchain.append([last_transaction, transaction_amount])
# The purpose of the following function is to: 1. Get user input at console 2. return the user input value as a float
def get_transaction_value():
""" It returns the input of the user (a new transaction amount) as a float"""
user_input = float(input("Amount: ")) #input() function is used to get a user input at console
return user_input
def get_user_choice():
user_input = input("Your choice: ")
return user_input
def print_blockchain_elements():
# The following loop goes through the list items and print each item individually
# Then, the internal if statement verifies that the block/item parsed by for loop is indeed the next item in the list (by using indexes)
for block in blockchain:
print('Outputting block:')
print(block)
if block == blockchain[index_ul]:
print("block matches!")
index_ul += 1
# Get the first transaction input and add the value to the blockchain
tx_amount = get_transaction_value() #here I define a variable "tx_amount" with the value = to the result of the "get_user_input() function"
add_value(tx_amount) # Here, i call the function , specifying a value only for the "transaction_amount" variable of the function,
# the second argument of the function gets its default value last_transaction=[1]
while True:
print("Please choose: ")
print("Press 1 for: Add a new transaction value")
print("Press 2 for: Outputting the blockchain blocks")
user_choice = get_user_choice()
if user_choice == "1":
tx_amount = get_transaction_value()
add_value(tx_amount, get_last_blockchain_item())
else:
print_blockchain_elements()
print(blockchain)
'''
