1 / 13

Scoping and Namespaces

Scoping and Namespaces. CSIS 1595: Fundamentals of Programming and P roblem Solving 1. Namespaces. Namespace: List of all variables and their current values Maintained by Python environment Example:. Namespaces and Functions. Each function has different namespace

denim
Download Presentation

Scoping and Namespaces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Scoping and Namespaces CSIS 1595: Fundamentals of Programming and Problem Solving 1

  2. Namespaces • Namespace: • List of all variables and their current values • Maintained by Python environment • Example:

  3. Namespaces and Functions • Each function has different namespace • Variable in function has no effect on same variable in any other function • Like two “separate universes” Spock in main program Spock in separate function

  4. Namespace Example

  5. Arguments and Namespaces • Arguments to functions are also local to a namespace • Example: Fahrenheit to Celsius program • Note that f and c are differentin function, main program

  6. Arguments and Namespaces • Key idea: Does not matter whether same or different variable names used in functions • Will be treated as different variables regardless • Example: Two versions of fahreheit2celsius program • Both do the same thing

  7. Passing Arguments by Value • Key idea: • Variables not passed or returned • Only their values are passed/returned • In both cases the valueof 50 passed and the value of 10 returned

  8. Namespaces and Functions • Why is this important? • Same function may be called from multiple places with different arguments • Example: “Largest of 4 numbers” program • Programs often created by hundredsof programmers • Each creates set of functions • Should not have to worry about what variables other programmers are using! • Functions often put in separate files (modules) • No main program associated with it!

  9. Functions Calling Functions • Separate namespace created for each call

  10. Activation Stack • Each current namespace = “activation record” • Maintained on “stack” of activation records • When function called, its namespace pushed on top of stack • When return from function, that namespace removed • Return to function immediately below it on stack

  11. Stack for Population Program compute_population print_line compute_population print_line get_years print_table print_table print_table print_table print_table print_table print_table print_table Main program Main program Main program Main program Main program Main program Main program Main program Main program Main program Main program

  12. Scoping • Key idea: Namespace only exists while function active • Scope of variable = function it is defined in • Does not exist outside of its scope(error if referenced)

  13. Scoping and Global Variables • Exception: Functions may refer to variables in main • Exception to the exception: If value assignedin function it becomes local to function • Just avoid doing this! Prints 3 Still 3

More Related