Introduction to Python

1. Introduction to Python (for C++ programmers)

2. Background Information • History • created in December 1989 by Guido van Rossum • Interpreted • Dynamically-typed language • no int, char, long nonsense • Object Oriented • Current versions are 2.7.3 and 3.3.0 • not backwards compatible

3. Terms • Pythonic • hard to define • programming in a way that lends itself well to the Python language • Pythonista – a person who codes in a pythonic way

4. The Zen of Python • Beautiful is better than ugly. • Explicit is better than implicit. • Simple is better than complex. • Complex is better than complicated. • Flat is better than nested. • Sparse is better than dense. • Readability counts. • Special cases aren't special enough to break the rules. • Although practicality beats purity. • Errors should never pass silently. • Unless explicitly silenced. • …

5. Syntax • Indentation • Colon on the line before indented block • No Braces

6. Types of Quotes • Double quote – “string” • Single quotes – ‘string’ • Triple quotes –

7. Let’s Dive In! • Hello World • A more interesting Hello World

8. Data Types • Numeric Types — int, float, long, complex • List – [] • Tuple – () More About Tuples • Dictionary – {} dict • string • set, frozenset • Mutable vs. Immutable • Indexing (slicing, step slicing) • Heterogeneous

9. C++ <=> Python

10. for • iterate through stuff for var in iterable: do_something

11. in • Check for membership • Iterating through lists (as in the ‘for’ example)

12. is vs. == • Remember Python is an OOPL? • The ‘is’ keyword checks if two variable names point to the same memory. • == checks the value. Uses the __eq__ function in classes.

13. Pythonic Programming The idiomatic way to perform an operation on all items in a list in C looks like this: for (i=0; i < mylist_length; i++) { do_something(mylist[i]); } The direct equivalent in Python would be this: i = 0 while i < mylist_length: do_something(mylist[i]) i += 1 That, however, while it works, is not considered Pythonic. It's not an idiom the Python language encourages. We could improve it. A typical idiom in Python to generate all numbers in a list would be to use something like the built-in range() function: for i in range(mylist_length): do_something(mylist[i]) This is however not Pythonic either. Here is the Pythonic way, encouraged by the language itself: for element in mylist: do_something(element)

14. Functions • Functions are objects too • Can return multiple values using tuple unpacking • Can pass in arbitrary number of elements

15. Useful Builtin Functions • len() • range() and xrange() • enumerate() • map() • zip() • any() and all() • dir() • http://docs.python.org/py3k/library/functions.html

16. List Comprehension and Generators • List comprehension makes a list (subscriptable, iterable) • Generators • not a tuple • iterable • calculation gets done on demand (when iterated) • can’t subscript

17. Python 2 vs. Python 3 • print • range and xrange • raw_input and input • division • 2 does integer division. Use // to do floating • 3 does floating point. Use // to do integer • str and bytes • Unicode • __future__ • Full changes at http://bit.ly/djYOVa

18. Modules (Importing)

19. Gotchas • Other languages have "variables“ • Mixing tabs and spaces or inconsistent indentation • no i++ notation; use i += 1 • http://zephyrfalcon.org/labs/python_pitfalls.html

20. Exceptions and Classes • for another day • just know they exist

21. Tips and Tricks • Swap Values • Chained comparisons a < b < c is the same as a < b and b < c • easy_install - setuptools 0.6c11 • http://pypi.python.org/pypi • pdb - The Python Debugger • profile

22. Learning Python • http://python.org/ • Great documentation for every version! • help() • ipython • python shell • tab-completion • ? and ?? • http://bit.ly/2noLNE • http://pythontutor.com/ • http://www.doughellmann.com/PyMOTW/index.html