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Why Write Computer Programs? Chapter 1: Programming Basics, Python History and Program Components CS10061 – Introduction to Computer Programming Chapter 1: Getting Started 1 To assist with a complex situation that requires a human touch Managing livestock Patient simulators Forensics Weather predictions Chapter 1: Getting Started Why Write Computer Programs? Why Write Computer Programs? To aid with creative thought and higher-level To perform routine or repetitive tasks that organization follow a clear series of steps or work with electronic information Virtual dancers Online academic classes Package deliveries Games Robotics or smart devices Banking transactions Chapter 1: Getting Started 2 3 Chapter 1: Getting Started 4 1 Programming Basics Program Basics – Cont’d: A computer program contains instructions Are all programming languages the same? written by humans and understandable by computers (statements vs. instructions). A programming language is used to write a computer program. Chapter 1: Getting Started 5 No, there are many differences Machine-like vs. English-like Compiler (source code) vs. interpreted (dynamic) Commercial vs. open-source Platform dependent vs. platform independent Chapter 1: Getting Started Program Basics – Cont’d: Python’s History How do you get started with programs? Developed by Guido van Rossum Identify the task to solve or automate Released in 1991 Determine the programming language to use Named after the English comedy troupe Install the programming language Monty Python (many unique references), but Read the documentation and learn the jargon the current mascot is a little green snake Navigate the working environment (IDLE) Chapter 1: Getting Started 7 Chapter 1: Getting Started 6 8 2 Why Use Python? Python IDLEs Easy to learn and easy to use Python’s IDLEs are working environments for Powerful and efficient (no compilation) programmers. Statements are entered: Open-source and free Platform independent Integrates or embeds easily with other At a command prompt (>>>) In a text editor There are two main IDLEs in Python Interactive (Shell) Mode (command prompt) Script Mode (text editor) programming languages Object-oriented ability is optional Chapter 1: Getting Started 9 Chapter 1: Getting Started Python Interactive (Shell) Mode Python Script Mode Utilizes the command prompt (>>>) Environment is like a text editor (Notepad) Results are displayed to the screen Enables the writing, saving and editing of immediately Not usable with programs that are already created and saved Automatically invoked for screen output when a saved program is run Useful for trying out correct syntax programs Invoke by File New Window from the interactive (shell) mode Save by File Save As 10 Name the file and add the “.py” extension Run with Edit Run Script Results are displayed in a shell window Chapter 1: Getting Started 11 Chapter 1: Getting Started 12 3 Program Components Program Components Statements do something In English, they convey complete thoughts In Python, they give complete instructions Expressions are something with a value Denoted in green Part of a statement Values may be: Commands force action Denoted in orange Case sensitive, specifically lowercase Part of a statement Strings or series of characters Numbers, a particular number Evaluations, say 3 + 1 Example: print “Hello, World” Example: print 17 Example: print “Hello, World” Example: print 3 + 1 Command Chapter 1: Getting Started 13 Syntax errors result when the interpreter Misspellings of commands Example: prnt “Hello, World” produces SyntaxError: invalid syntax The error displayed generally indicates what is wrong with the statement Familiarize yourself with what syntax errors mean so errors may be fixed quickly Chapter 1: Getting Started Evaluation 14 Program Components: Syntax Errors – Cont’d. Misspellings of commands Incorrect command usage Other typographical mistakes Number Chapter 1: Getting Started Program Components: Syntax Errors cannot understand a statement String 15 The cursor highlights the last character of the statement Chapter 1: Getting Started 16 4 Program Components: Syntax Errors – Cont’d. Program Components: Syntax Errors – Cont’d. Incorrect command usage Other typographical mistakes Example: Hello produces SyntaxError: invalid token Traceback (most recent call last): File "<pyshell#0>", line 1, in ? hello NameError: name 'hello' is not defined Example: prnt “Hello, World produces The word “World” is highlighted to indicate the “token” A new command prompt is displayed Chapter 1: Getting Started 17 Chapter 1: Getting Started 18 Program Components Program Components Comments are used for program Blank lines Used to separate blocks of related statements Aids in reading the source code Ignored by the interpreter at program execution documentation Denoted in red Assists with understanding the code (original developer or subsequent programmers) Preceded by “#” which is ignored by the interpreter at program execution Good programming practice dictates the use, especially as the program “header” Chapter 1: Getting Started Prompts Used to ask the user for input Forces the console window to remain open 19 Example: raw_input(“\n\nPress the enter key to exit.”) Chapter 1: Getting Started 20 5