NameError: name 'xx' is not defined
Python knows the purposes of certain names (ex. built-in functions ). Other names are defined within the program (ex. variables). If Python encounters a name that it doesn't recognize, you'll probably get NameError: global name 'xx' is not defined error. In most cases, this error is triggered when Python sees a variable name (Global or Local) and doesn't know what it's for. These errors can happen if you forget to initialize a variable , if you misspell a variable, or if you misspell a reserved word such as "True". Before you use the global variable in your function for reading, it must be first initialized somewhere: either outside of the function or inside it.