11 scripting languages

11 scripting languages

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  1 Scripting Languages CIS*2450 Advanced ProgrammingConcepts
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  2 Scripting Languages • Scriptinglanguages are generally interpreted instead of compiled. – Immediate execution allows for rapid development and change. • “Easy to learn” and have support for high-level structures and libraries. – Much of the initial work for many applications has been done and is available in libraries. – Structures such as lists and dictionaries usually builtin
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  3 Scripting Languages • Pythonuses combination of compilation and interpretation: – The source code is converted to an intermediate form called byte code in a step similar to compilation. – The byte code is executed by an interpreter. – This improves performance over purely interpreted systems.
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  4 Source Executable Execution Compiler Run Source Execution Interpreter Source Byte Code Execution Compiler Interpreter Byte Code Execution Interpreter Execution Compiled Execution
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  5 Scripting Languages • Scriptinglanguages are often used to combine the functionality of other programs. – They act as glue. • This allows the script to act as the intermediary between programs and pass information between them.
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  6 Extending • External programscan be used to increase the functionality of the scripting language by binding existing programs to it – This is called extending. • This allows function calls to be made directly to the compiled programs instead of through command interface (stdin/stdout)
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  7 Dynamic Typing • Scriptinglanguages often support dynamic typing. • The system manages the types of variables without the programmer’s explicit input on matters of length and type declarations. • Some languages treat all variables as strings and modify them when non-string operations occur with the variable.
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  8 Dynamic Typing • Thiscan lead to type mismatches when a variable is assigned a type that is not expected. • It can also cause problems if a variable name is misspelled. – Results in two different variables existing when only one was intended.
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  9 Memory Management • Automaticmemory management controls the allocation and freeing (garbage collection) of memory on demand. – Objects can grow and shrink as needed and are removed when no longer necessary.
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  10 Object-Oriented • Many scriptinglanguages are starting to adopt object-oriented structures. • Traditional scripting languages tend to become difficult to manage when used to write larger programs and the inclusion of OO is an attempt to address the problem. – E.g. Python, incrTCL, Object Oriented Perl
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  11 OO and Python •Python supports most OO concepts: – Ability to create multiple name spaces (scope). • Each object contains its own name space. – Polymorphism • Methods change based on their class. – Operator Overloading • Operators given multiple meanings. – Multiple Inheritance • A class can be the product of multiple parents.
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  12 Dynamic Code Creation •Many scripting languages can dynamically create and execute code during the execution of the script. – This generally cannot be done by a non- scripting language. a = 10 x = “print a” exec(x)
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  13 Data Structures • Mostmodern scripting languages have built-in support for high level data structures. – Associative arrays • Also called dictionaries or hash tables. – Lists