1. Global scope value can not be changed in function.

2. We can define a global variable in a function by using global.

3. Rules of using variable:

• First start with the local scope, if any. If the variable is defined here, use the value.
• Look at any enclosing scopes, starting with the innermost. These are "outside" local scopes. If the variable is defined in any of them, use the value.
• Look in the global scope. If the variable is there, use the value.
• Finally, look in the built-in functions.
• If no value is found, an error will be thrown.

Regular Expression(for extract number from a long string):

1. 

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