OSC python programming pot

Python Programming Science & Technology Support Group 20-21 February 2007 Python Programming Instructor Peter G. Carswell Supercomputer Resource Specialist Ohio Supercomputer Center pete@osc.edu (614) 292-1091 3Python Programming Table of Contents • Introduction • The “Not-So-Full” Monty – Mechanics of using Python – Variables, Data Types and Operators – Programming statements – Python Functions – Using Python Modules – Everything is an Object – Classes and Objects – Operator Overloading – Constructors 4Python Programming What is Python? • NOT an acronym (Thank goodness!). Named after Monty Python • A compiled/interpreted mid-level language – Not only used for scripting tasks •Extremelyuseful for a huge variety of programming tasks (Modules) • Easy to “glue” with other languages (C, C++, Java …) • Under the hood: Object Oriented • Commonly in use: Versions 2.3 and 2.4 –Use python –V to see the version • Python is portable • Python is free! • Home Page: www.python.org 5Python Programming Basic Operation • Python is both an interpreted and a compiled language • When run, the program is first read and “compiled” in memory – Not a true compilation to native machine instructions – Python source code converted to byte code (platform-independent) – Some optimizations are performed, e.g. • eliminating unreachable code • reducing constant expressions • loading library definitions • Second stage is line-by-line execution via the interpreter PVM (Python Virtual Machine) – analogous to Java VM • Much faster than fully interpreted languages, such as the shell • No object code – But byte code saved in a file called prog.pyc Python Programming Running Python 7Python Programming To use Python: Interactive • Type python in a shell window and start typing in commands at the Python prompt >>>. The results of the commands will be seen immediately. • Workshop examples will be for Python on Unix/Linux system. [piv-login1]% python Python 2.2.3 (#1, Feb 2 2005, 12:20:51) [GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-49)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> >>> print "Hello World! (with respect)“ #Basic output command Hello World! (with respect) >>> a=34.5 # No variable type declaration >>> a # To see contents of variable, type its name 34.5 >>> a*5.6 193.2 >>> z=a/33.3 >>> print '%7.2f' %(z) #Formatting Output 1.04 >>> ^D #How to exit the Python session $ 8Python Programming Ways to use Python: Shell Scripts • A shell script is just a series of python commands entered line-by-line into a file. By typing the name of the shell script after the python executable, all the commands will be run in order. • By convention files composed of Python commands have the suffix py. Let’s say all the commands on the previous slide have been put into a file rabbit.py. Here’s how it would be run: Notice that only the text directly written out to stdout will appear on your monitor $ python rabbit.py Hello World! (with respect) 1.04 $ 9Python Programming Ways to use Python: Executable Scripts • Say you want to run your Python script directly at the system prompt. (Just like an operating system command). This requires two steps – Make the first line in the rabbit.py file #!<full pathname of Python executable> – Second, give rabbit.py executable permission $ chmod u+x rabbit.py • Now the rabbit file looks like this: • To run the commands in the rabbit.py file, just type its name at the system prompt #!/usr/local/bin/python print "Hello World! (with respect)" a=34.5 a a*5.6 z=a/33.3 print '%7.2f' %(z) $ rabbit.py Hello World! (with respect) 1.04 Python Programming Variables, Data Types and Operators [...]... objects … Python Programming 11 Data Types • Python has five built-in, core data types Listed here in the order in which they will be covered Numbers Strings Lists Dictionaries Tuples Python Programming 12 Numbers in Python Type Examples Decimal Integers 10 -235 Octal and Hexadecimal Integers 034723 0x3DE56A Long Integers (unlimited size) 777888207468890L Floating-Point 3.45 Complex 6.2+3J Python Programming. .. y Addition, Subtraction x-y Python Programming 14 Operator Precedence & Parenthetical Override $ python Python 2.2.3 (#1, Oct 26 2004, 17:11:32) [GCC 3.2.3 20030502 (Red Hat Linux 3.2.3-47)] on linux2 Type "help", "copyright", "credits" or "license" for more information >>> a=40 >>> b=3 >>> c=75 >>> a*b+c 195 >>> a*(b+c) 3120 >>> $ Python Programming 15 Python Division Python 2.2.3 (#1, Oct 26 2004,... well 3.0 >>> divmod(9,4) # Returns (x/y,x%y) tuple (2,1) $ Python Programming 16 Alternative Integer Bases >>> num=4578 >>> int(num) 4578 >>> int(67.345) 67 >>> round(67.899) 68.0 >>> oct(num) '010742' >>> hex(num) '0x11e2' >>> #Truncating Conversion #Can “round-up” #Octal literals have leading 0 #Hex literals have leading 0x Python Programming 17 Python Long Integers • Long integers marked with a trailing... twice We will see later that some Python variables can are quite large – This shortened syntax will cause the compiler to automatically pick the optimized technique for performing the combined operations This advantage will have a greater effect on the more sophisticated data types to come • Note for C/C++ users: no increment/ decrement operators (++, ) in Python Python Programming 21 “Augmented” Assignment... Truth shall set you free >>> Python Programming 25 String Operators Expression What Happens str1 + str2 Concatenation str *n Replication (n is an integer) n*str str[i] String element with index i str[i:j] Substring of consecutive elements (i to j-1) len(str) Number of characters in a string max(str) Maximum element (ASCII value) min(str) Minimum element (ASCII value) Python Programming 26 Working with... print rur[-3] # Negative index => relative to end 3 # of string [ length(rur)+i ] >>> print rur[-11:-4] Droid Python Programming 27 Finish theWork >>> print len(rur) 19 >>> print max(rur) t >>> print min(rur) # Number of elements # ASCII code for ‘t’= 116 # ASCII code for (space) ‘ ‘= 32 >>> Python Programming 28 Strings playing well with others … • • • The addition symbol ‘+’ is overloaded: it can add... wait for input Clever way of encouraging prompts Prompts are optional, though All input entered will be treated as a string by your Python program Must use the conversion commands on the previous slide for other types Python Programming 33 The read.py Script #!/usr/bin /python year=raw_input("Please enter a year:") year=int(year) #convert input string to int ten=year+10 print "A decade later will be",... r=(x**2+y**2)**0.5 print "Distance from origin is", r Python Programming 34 An Input Session $ read.py Please enter a year:1963 A decade later will be 1973 Enter x coord: 3.0 Enter y coord: 4.0 Distance from origin is 5.0 $ read.py Please enter a year:2260 A decade later will be 2270 Enter x coord: 13.4 Enter y coord: 56.2 Distance from origin is 57.7754273026 Python Programming 35 More Refined Input • There is... variable from the variable_list Example: print ”Out %15s %5d %10.2f\n” % (a,b,c) Control string – List of items to be printed See printf man page for further details >> man printf Python Programming 32 Interlude: Can we provide input to Python programs? • • • Yes The most basic of reading commands is called (aptly enough) raw_input() When raw_input() is executed, the program stops and waits for input from... precision In this #case ~15 decimal places (8 byte word) >>> print power 1.23114441334 >>> "%e" % power '1.231144e+00' >>> "%1.5f" % power '1.23114' >>> Python Programming 19 Complex Numbers • A feature* of some implementations of complex numbers in python is that the coefficient must be represented in decimal format, i.e 5.0j not 5j *feature is a term used by programmers to make excuses for programs . use: Versions 2.3 and 2.4 –Use python –V to see the version • Python is portable • Python is free! • Home Page: www .python. org 5Python Programming Basic Operation • Python is both an interpreted. prog.pyc Python Programming Running Python 7Python Programming To use Python: Interactive • Type python in a shell window and start typing in commands at the Python prompt >>>. The results. Center pete @osc. edu (614) 292-1091 3Python Programming Table of Contents • Introduction • The “Not-So-Full” Monty – Mechanics of using Python – Variables, Data Types and Operators – Programming