问题
This code runs without errors. But in the function find_available_filenumber the variable render_folder isn't declared. So my question is why this doesn't produce an error?
If I remove full_filename as a parameter, I get the error:
UnboundLocalError: local variable 'full_filename' referenced before assignment.
I don't understand why this doesn't also happen with render_folder, in my code example below:
import bpy
import os
#Functions
def find_available_filenumber(full_filename):
file_number = 1
while os.path.exists(render_folder + "\\" + full_filename):
file_number += 1
full_filename = create_full_filename(filename, file_number)
return file_number
def create_full_filename(filename, file_number):
file_extension = ".avi"
full_filename = filename + "_" + str(file_number) + file_extension
return full_filename
#Paths and names
project_folder = "F:\\06_MotionPath_Dev\\"
os.chdir(project_folder)
render_folder = "Render\\QuickRenderAddon"
filename = bpy.context.scene.name #Returns "QuickRenderAddon"
full_filename = create_full_filename(filename, 1)
filepath = render_folder + "\\" + full_filename
available_number = find_available_filenumber(full_filename)
print("Avail nmb: " + str(available_number))
回答1:
Ah yes the classic "Referenced before Assignment"
I wrote some example code to show what is going on.
test = "toast!"
toast = "test!"
def func():
print test
print toast
func()
The output of the above is
toast!
test!
This shows that we can read global variables, but what about writing to them? I don't want 'toast' to be 'test!' anymore, but rather 'bread+toaster!'. Let's write this out.
test = "toast!"
toast = "test!"
def func():
print test
toast = "bread+toaster!"
print toast
func()
print toast
This outputs
toast!
bread+toaster!
test!
You'll notice that we were able to print the locally assigned variable, but the global variable did not change. Now, let's look at another example.
test = "toast!"
toast = "test!"
def func():
print test
print toast
toast = "bread+toaster!"
print toast
func()
print toast
This will throw the error
UnboundLocalError: local variable 'toast' referenced before assignment
Why? Because you're later declaring your variable 'toast' as a local variable. Python notices this and stops the code to prevent errors. You setting 'toast' later is not changing the global variable, but rather declaring a local one within the function called 'toast'.
How can you fix this?
The first would be to add a global clause inside your function
test = "toast!"
toast = "test!"
def func():
global toast
print test
print toast
toast = "bread+toaster!"
print toast
func()
print toast
This outputs
toast!
test!
bread+toaster!
bread+toaster!
You can also modify your code into a class structure, as such.
class bread():
def __init__(self):
self.test = "toast!"
self.toast = "test!"
def func(self):
print self.test
print self.toast
self.toast = "bread+toaster!"
print self.toast
b = bread()
b.func()
In my opinion, classes are the best solution as it will increase modularity and help you reduce spaghetti code.
回答2:
Edit: Ignore me, I'm on mobile, so I didn't properly read.
The error states "referenced before assignment". In other words, you are trying to read a value from that variable before you have written a value to it.
I have a feeling this error is being cause in your while conditional, as you are checking the value before writing to it in the body of the while loop.
回答3:
This code runs without errors. But in the function find_available_filenumber the variable render_folder isn't declared. So my question is why this doesn't produce an error?
This is because render_folder is declared at the time find_available_filenumber is called, even though its not declared when your function is defined.
来源：https://stackoverflow.com/questions/27093089/why-does-one-of-my-variables-doesnt-need-declaration-while-the-other-one-does