python_lectures_1

Introduction to language - startup
pczaal2: python Python 2.7.5 (default, Nov 3 2014, 14:26:24) [GCC 4.8.3 20140911 (Red Hat 4.8.3-7)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> 2+2 4 >>> # This is a comment ... 2+2 4 >>> 2+2.0 # and a comment on the same line as code 4.0 >>> (50-5*6)/4 5 >>> width = 20 # assignment, no type declaration >>> height = 5*9 >>> width * height 900 >>> x = y = z = 0 # zero x, y and z >>> y 0 >>> n Traceback (most recent call last): File "<stdin>", line 1, in <module> NameError: name 'n' is not defined
Introduction to language - scripts
2+2 # This is a comment 2+2 2+2.0 # and a comment on the same line as code (50-5*6)/4 width = 20 # assignment, no type declaration height = 5*9 width * height x = y = z = 0 # zero x, y and z y
Python in radio astronomy
• CasaPy (Casa) - AIPS++, default system for EVLA and ALMA data analysis. • ParselTongue - call AIPS tasks from Python • PYGILDAS (GILDAS) - IRAM data analysis software ported to Python • BoA (Bolometer Analysis Package) for LABOCA on APEX and other bolometers • APECS (APEX control software)
Introduction to language - start
Windows
Files that have the extension .py are known as Python scripts. In Windows and Mac OS, these files will appear to be "clickable", i.e. will appear to be files that you can open by clicking them with the mouse. It is not recommended that you open these files by clicking on them. Why? Because quite often the result can be unpredictable. Instead, start IDLE and open Python scripts inside an IDLE session.
• Computational physics • ALPS (Algorithms and Libraries for Physics Simulations) • …
Introduction to language - start
Linux •At command line: python myscript.py •With script: chmod, #!/usr/bin/env python •At python prompt: execfile(‟somefile.py‟) •At ipython prompt: %run somefile.py
Python in optical astronomy
• STScI PyRAF (IRAF) + additional Python only routines • ESO PyMIDAS (MIDAS) • STScI PyFITS (access to FITS files) • Astro-WISE (widefield imaging system) • Pyephem - solar system ephemeris • LSST will use Python/C+ • …
• Ease of use • Speed of development • Encourages scripting, rather than one-off analysis • Permanent record • Repeatability
Why not python?
• If you want fastest possible performance • Highly parallel code • Need low-level control
• Python programmers in demand • Easy introduction to general programming concepts Why not? • Existing code for your project in another language, but still…
Why learn Python?
• • • • Less stress Get more science done Widely used and growing popularity Throughout academia and industry
– NASA, AstraZeneca, Google, Industrial Light & Magic, Philips,… – Web services, engineering, science, air traffic control, quantitative finance, games, education, data management, …
Introduction to language - numbers
>>> 10 + 3 13 >>> 10 - 3 7 >>> 10 * 3 30 >>> 10 / 3 3 >>> 10 // 3 3 >>> 10 % 3 1 >>> 10**3 1000 >>> 10 + 3 * 5 # *,/ then +,25 >>> (10 + 3) * 5 65 >>> -1**2 # -(1**2) -1 >>> 10.0 + 3.0 13.0 >>> 10.0 - 3.0 7.0 >>> 10.0 * 3 30.0 >>> 10.0 / 3 3.3333333333333335 >>> 10.0 // 3 3.0 >>> 10.0 % 3.0 1.0 >>> 10.0**3 1000.0 >>> 4.2 + 3.14 7.3399999999999999 >>> 4.2 * 3.14 13.188000000000001
Why Python is great
• • • • • • • • • • Designed to be easy to learn and use – clear syntax Well documented Powerful, flexible, fully-featured programming language „Batteries included‟ Comprehensive scientific tools Fast Interpreter, introspection Runs everywhere Completely free You already have it
• KAT-7 CMS is in Python
• Presto - pulsar search and analysis suite; most recent routines in Pytho
Python in physics
• CERN
– PyROOT (research engine for high energy physics) – PyMad (simulate particle accelerators)
• Can write in a text editor and copy and paste into interpreter • Can save and execute from command line:
$ python test.py
• Can save and use interactively in future sessions (import)