Structured programming

Structured programming is a programming paradigm aimed at improving the clarity, quality, and development time of a computer program by making extensive use of the structured control flow constructs of selection (if/then/else) and repetition (while and for), block structures, and subroutines.

It emerged in the late 1950s with the appearance of the ALGOL 58 and ALGOL 60 programming languages,[1] with the latter including support for block structures. Contributing factors to its popularity and widespread acceptance, at first in academia and later among practitioners, include the discovery of what is now known as the structured program theorem in 1966,[2] and the publication of the influential "Go To Statement Considered Harmful" open letter in 1968 by Dutch computer scientist Edsger W. Dijkstra, who coined the term "structured programming".[3]

Structured programming is most frequently used with deviations that allow for clearer programs in some particular cases, such as when exception handling has to be performed.

Conditional (computer programming)

In computer science, conditional statements, conditional expressions and conditional constructs are features of a programming language, which perform different computations or actions depending on whether a programmer-specified boolean condition evaluates to true or false. Apart from the case of branch predication, this is always achieved by selectively altering the control flow based on some condition.

In imperative programming languages, the term "conditional statement" is usually used, whereas in functional programming, the terms "conditional expression" or "conditional construct" are preferred, because these terms all have distinct meanings.

Although dynamic dispatch is not usually classified as a conditional construct, it is another way to select between alternatives at runtime.

In conditional statement, inequality and equality signs are implemented, such as <, > ,=<, => , =, or !=. Conditional statements are started with "If" and followed by "else", "elseif", or "then" ("then" can be omitted). Based on the type of language, illustration of such sign could be varied.

    If/Then/Else:
            If A = B (Then)
                Operation when A and B are equal
             Else 
                Operation when A and B are not equal

    If/Elseif/Else:
            If A < B
                Operation when A is less than B
             Elseif A > B
                Operation when A is greater than B
             Else
                Operation when A is equal B 
                (A is not less than B AND A is not greater than B)

    Default Else:

Data validation

In computer science, data validation is the process of ensuring data has undergone data cleansing to ensure they have, that is, that they are both correct and useful. It uses routines, often called "validation rules", "validation constraints", or "check routines", that check for correctness, meaningfulness, and security of data that are input to the system. The rules may be implemented through the automated facilities of a data dictionary, or by the inclusion of explicit application program validation logic of the computer and its application.

This is distinct from, which attempts to prove or disprove the correctness of algorithms for implementing a specification or property.

Exception Handling

In computing and computer programming, exception handling is the process of responding to the occurrence of exceptions – anomalous or exceptional conditions requiring special processing - during the execution of a program. In general, an exception breaks the normal flow of execution and executes a pre-registered exception handler; the details of how this is done depend on whether it is a hardware or software exception and how the software exception is implemented. It is provided by specialized programming language constructs, hardware mechanisms like interrupts, or operating system (OS) inter-process communication (IPC) facilities like signals. Some exceptions, especially hardware ones, may be handled so gracefully that execution can resume where it was interrupted.

An alternative approach to exception handling in software is error checking, which maintains normal program flow with later explicit checks for contingencies reported using special return values, an auxiliary global variable such as C's errno, or floating point status flags. Input validation, which preemptively filters exceptional cases, is also an approach.

Python syntax and semantics/exceptions - EAFP vs. LBYL

The syntax of the Python programming language is the set of rules that defines how a Python program will be written and interpreted (by both the runtime system and by human readers). The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages.

Defensive programming

Defensive programming is a form of defensive design intended to ensure the continuing function of a piece of software under unforeseen circumstances. Defensive programming practices are often used where high availability, safety, or security is needed.

Defensive programming is an approach to improve software and source code, in terms of:

General quality – reducing the number of software bugs and problems. Making the source code comprehensible – the source code should be readable and understandable so it is approved in a code audit. Making the software behave in a predictable manner despite unexpected inputs or user actions. Overly defensive programming, however, may safeguard against errors that will never be encountered, thus incurring run-time and maintenance costs. There is also a risk that code traps prevent too many exceptions, potentially resulting in unnoticed, incorrect results.