An Introduction to the Zen of Python

An introduction to the Python programming language organized around "The Zen of Python".

Transcript

1. An Introduction to the Zen of Python Doug Hellmann February, 2011 Friday, February 18, 2011
2. The Zen of Python by Tim Peters •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. •In the face of ambiguity, refuse the temptation to guess. •There should be one – and preferably only one – obvious way to do it. •Although that way may not be obvious at first unless you're Dutch. •Now is better than never. •Although never is often better than *right* now. •If the implementation is hard to explain, it's a bad idea. •If the implementation is easy to explain, it may be a good idea. •Namespaces are one honking great idea – let's do more of those! Friday, February 18, 2011
3. Beautiful is better than ugly. • Write programs for human readers • Simple expression syntax • Consistent syntax and behavior Friday, February 18, 2011
4. 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Simple Expressions Friday, February 18, 2011
5. 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Simple Expressions Friday, February 18, 2011
6. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
7. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
8. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
9. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
10. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
11. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
12. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
13. Simple Expressions 1 i = 5 + 5 2 3 s = 'literal string' 4 5 m = """multi-line 6 string 7 """ 8 9 us = u'üñîçø∂é string' 10 11 vals = [ 1, 3, 5, 7, ] 12 vals[0] 13 14 t = ('a', 1, vals, None) 15 t[1] 16 17 d = { 'a':'a value', 18 'b':'b value', 19 } 20 d['a'] 21 22 if a or b: 23 do_something() 24 Friday, February 18, 2011
14. Explicit is better than implicit. • Boolean type • No “hidden” loop variables • Use “self” to refer to object inside a method Friday, February 18, 2011
15. Boolean Values 1 t = True 2 f = False 3 4 if t: 5 print 't is true' 6 7 if not f: 8 print 'f is false' 9 10 a = t or f 11 b = t and f 12 13 print a 14 print b $ python booleans.py t is true f is false True False Friday, February 18, 2011
16. for loops 1 print 'Numbers:' 2 3 for i in range(5): 4 print i 5 6 print 7 print 'Letters:' 8 9 for c in [ 'a', 'b', 'c' ]: 10 print c $ python for_loop.py Numbers: 0 1 2 3 4 Letters: a b c Friday, February 18, 2011
17. Defining a Class 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
18. Defining a Class 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
19. Defining a Class 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
20. Defining a Class 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
21. Defining a Class 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
22. Simple is better than complex. • Garbage collection • print statement • Interactive interpreter for experimentation Friday, February 18, 2011
23. Printing 1 # -*- encoding: utf-8 -*- 2 3 print 'string:', 'string' 4 5 print 'unicode:', u'üñîçø∂é string' 6 7 print 'number:', 5 * 5 8 9 my_list = [ 1, 'a', None ] 10 print 'list:', my_list 11 12 my_dict = { 'a':'a value', 'b':'b value' } 13 print 'dict:', my_dict $ python printing.py string: string unicode: üñîçø∂é string number: 25 list: [1, 'a', None] dict: {'a': 'a value', 'b': 'b value'} Friday, February 18, 2011
24. Printing, with printf-style Formatting 1 # -*- encoding: utf-8 -*- 2 3 my_list = [ 1, 'a', None ] 4 my_dict = { 'a':'a value', 'b':'b value' } 5 6 args = ('string', u'üñîçø∂é string', 5 * 5, 7 my_list, my_dict) 8 9 print ''' 10 string : %s 11 unicode: %s 12 number : %d 13 list : %s 14 dict : %s 15 ''' % args $ python printing_with_format.py string : string unicode: üñîçø∂é string number : 25 list : [1, 'a', None] dict : {'a': 'a value', 'b': 'b value'} Friday, February 18, 2011
25. Interactive Interpreter Friday, February 18, 2011
26. Complex is better than complicated. • Do complex things in a “Pythonic” way • SciPy and NumPy for advanced science and math Friday, February 18, 2011
27. Interactive Graphic Environment SciPy, NumPy, matplotlib Friday, February 18, 2011
28. NumPy Performance 1 a = range(10000000) 2 b = range(10000000) 3 c = [] 4 for i in range(len(a)): 5 c.append(a[i] + b[i]) Standard Python 1 import numpy as np 2 a = np.arange(10000000) 3 b = np.arange(10000000) 4 c = a + b NumPy 5-10 seconds “nearly instantaneous” Friday, February 18, 2011
29. Flat is better than nested. • Wide variety of modules in standard library • Namespace is flat • No need to use long names: com.company.java.blah.blah Friday, February 18, 2011
30. Standard Library Modules: Networking • socket • select • SocketServer • BaseHTTPServer • asyncore • asynchat • xmlrpclib • SimpleXMLRPCServer Friday, February 18, 2011
31. Standard Library Modules: Internet Protocols • urllib • httplib • ftplib • smtpd • smtplib • poplib • imaplib • json Friday, February 18, 2011
32. Standard Library Modules: Command Line • getopt • optparse • argparse • fileinput • cmd • readline Friday, February 18, 2011
33. Standard Library Modules: Parallel Processing • subprocess • threading • multiprocessing • Queue Friday, February 18, 2011
34. Standard Library Modules: Databases • anydbm • pickle • shelve • sqlite3 Friday, February 18, 2011
35. Standard Library Modules: Miscellaneous • datetime • grp • pwd • profile • timeit • struct • ctypes • xml • tarfile • csv Friday, February 18, 2011
36. Sparse is better than dense. • Standard library stays “shallow” • http://pypi.python.org/ • Allows separate release schedules • pip (“pip installs Python packages”) Friday, February 18, 2011
37. Readability counts. • Whitespace for block structures • Minimal punctuation • Built-in documentation • Extensive online documentation at http://docs.python.org/ Friday, February 18, 2011
38. 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Code Blocks Friday, February 18, 2011
39. 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Code Blocks Friday, February 18, 2011
40. Minimal Punctuation 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
41. Minimal Punctuation 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
42. Inline Documentation 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
43. Inline Documentation 1 class MyClass(object): 2 """Class documentation. 3 """ 4 5 def __init__(self, arg1, arg2): 6 self.attr1 = arg1 7 self.attr2 = arg2 8 9 def do_something(self): 10 """Does some work and returns a value. 11 """ 12 return self.attr1 * self.attr2 13 14 obj = MyClass(1, 2) 15 print obj.do_something() Friday, February 18, 2011
44. Special cases aren’t special enough to break the rules. • Everything is an object • Methods and functions differ by scope • Dynamic typing and runtime attribute lookup • Most “features” in external modules Friday, February 18, 2011
45. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
46. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
47. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
48. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
49. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
50. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
51. String Methods 1 print ' string value '.split() 2 print ' string value '.strip() 3 print 'str' in ' string value ' 4 print 'CHUGALUG'.startswith('C') 5 print 'CHUGALUG'.endswith('end') 6 print ':'.join(['a', 'b', 'c']) $ python string_methods.py ['string', 'value'] string value True True False a:b:c Friday, February 18, 2011
52. Function and Method Scope 1 class MyClass(object): 2 3 def do_something(self, arg1, arg2): 4 return arg1 * arg2 5 6 def my_function(arg1, arg2): 7 return arg1 * arg2 Friday, February 18, 2011
53. Dynamic Attribute Lookup 1 class MyClass(object): 2 3 CLASS_ATTR = 'class value' 4 5 def __init__(self, arg): 6 self.attr = arg 7 8 o = MyClass('instance value') 9 print o.attr 10 print o.CLASS_ATTR $ python dynamic_attribute_lookup.py instance value class value Friday, February 18, 2011
54. Dynamic Typing 1 class A(object): 2 def do_something(self): 3 print 'in A' 4 5 class B(object): 6 def do_something(self): 7 print 'in B' 8 9 def work_on_obj(c): 10 c.do_something() 11 12 a = A() 13 b = B() 14 15 work_on_obj(a) 16 work_on_obj(b) $ python dynamic_typing.py in A in B Friday, February 18, 2011
55. Regular Expressions 1 import re 2 3 pattern = 'this' 4 text = 'Does this text match the pattern?' 5 6 match = re.search(pattern, text) 7 8 s = match.start() 9 e = match.end() 10 11 print 'Found :', match.re.pattern 12 print 'In :', match.string 13 print 'Range :', s, '-', e 14 print 'Substring:', text[s:e] $ python using_regex.py Found : this In : Does this text match the pattern? Range : 5 - 9 Substring: this Friday, February 18, 2011
56. Although practicality beats purity. • Multiple Programming Models • OOP • Procedural • Functional Friday, February 18, 2011
57. Procedural 1 def my_function(arg1, arg2): 2 """This function multiplies arg1 by arg2. 3 """ 4 return arg1 * arg2 5 6 results = [] 7 for i in range(5): 8 results.append(my_function(i, i)) 9 10 print results $ python procedural.py [0, 1, 4, 9, 16] Friday, February 18, 2011
58. Functional: List Comprehension 1 results = [ i*i for i in range(5) ] 2 3 print results $ python functional.py [0, 1, 4, 9, 16] Friday, February 18, 2011
59. Functional: List Comprehension 1 results = [ i*i for i in range(5) ] 2 3 print results $ python functional.py [0, 1, 4, 9, 16] Friday, February 18, 2011
60. Functional: List Comprehension 1 results = [ i*i for i in range(5) ] 2 3 print results $ python functional.py [0, 1, 4, 9, 16] Friday, February 18, 2011
61. Functional: List Comprehension 1 results = [ i*i for i in range(5) ] 2 3 print results $ python functional.py [0, 1, 4, 9, 16] Friday, February 18, 2011
62. Functional: Generator Expression 1 results = ( i*i for i in range(5) ) 2 3 print results 4 5 for i in results: 6 print i 1 $ python generator_expr.py 2 <generator object <genexpr> at 0x1004d20a0> 3 0 4 1 5 4 6 9 7 16 Friday, February 18, 2011
63. Functional: Generators 1 def gen_values(n): 2 for i in range(n): 3 yield i*i 4 5 print gen_values(5) 6 7 for i in gen_values(5): 8 print i 1 $ python generator.py 2 <generator object gen_values at 0x1004d2050> 3 0 4 1 5 4 6 9 7 16 Friday, February 18, 2011
64. Errors should never pass silently. • Exception-based error handling • Tracebacks aid debugging Friday, February 18, 2011
65. Exceptions and Tracebacks 1 def f(n): 2 if n > 0: 3 return n * f(n-1) 4 return 1 5 6 print f('5') $ python traceback.py Traceback (most recent call last): File ".../traceback.py", line 6, in <module> print f('5') File ".../traceback.py", line 3, in f return n * f(n-1) TypeError: unsupported operand type(s) for -: 'str' and 'int' Friday, February 18, 2011
66. Raising Exceptions 1 def f(n): 2 if not isinstance(n, int): 3 raise TypeError('n should be an int') 4 if n > 0: 5 return n * f(n-1) 6 return 1 7 8 print f('5') $ python raising.py Traceback (most recent call last): File ".../raising.py", line 8, in <module> print f('5') File ".../raising.py", line 3, in f raise TypeError('n should be an int') TypeError: n should be an int Friday, February 18, 2011
67. Raising Exceptions 1 def f(n): 2 if not isinstance(n, int): 3 raise TypeError('n should be an int') 4 if n > 0: 5 return n * f(n-1) 6 return 1 7 8 print f('5') $ python raising.py Traceback (most recent call last): File ".../raising.py", line 8, in <module> print f('5') File ".../raising.py", line 3, in f raise TypeError('n should be an int') TypeError: n should be an int Friday, February 18, 2011
68. Unless explicitly silenced. • Catch exceptions with try:except • Process • Convert • Ignore Friday, February 18, 2011
69. Catching Exceptions 1 def f(n): 2 if not isinstance(n, int): 3 raise TypeError('n should be an int') 4 if n > 0: 5 return n * f(n-1) 6 return 1 7 8 try: 9 print f('5') 10 except TypeError, err: 11 print 'Had an error:', err 12 else: 13 print 'No error' 14 finally: 15 print 'Always run' $ python catching.py Had an error: n should be an int Always run Friday, February 18, 2011
70. In the face of ambiguity, refuse the temptation to guess. • Coerce types only when not surprising • Cannot add strings and numbers • Can multiply them! Friday, February 18, 2011
71. Type Coercion 1 print 5 * 1.0 2 print 2 ** 100 3 print 2 * 'abc' 4 print 2 + 'abc' 1 $ python type_coercion.py 2 5.0 3 1267650600228229401496703205376 4 abcabc 5 Traceback (most recent call last): 6 File ".../type_coercion.py", line 4, in <module> 7 print 2 + 'abc' 8 TypeError: unsupported operand type(s) for +: 'int' and 'str' Friday, February 18, 2011
72. Type Coercion 1 print 5 * 1.0 2 print 2 ** 100 3 print 2 * 'abc' 4 print 2 + 'abc' 1 $ python type_coercion.py 2 5.0 3 1267650600228229401496703205376 4 abcabc 5 Traceback (most recent call last): 6 File ".../type_coercion.py", line 4, in <module> 7 print 2 + 'abc' 8 TypeError: unsupported operand type(s) for +: 'int' and 'str' Friday, February 18, 2011
73. Type Coercion 1 print 5 * 1.0 2 print 2 ** 100 3 print 2 * 'abc' 4 print 2 + 'abc' 1 $ python type_coercion.py 2 5.0 3 1267650600228229401496703205376 4 abcabc 5 Traceback (most recent call last): 6 File ".../type_coercion.py", line 4, in <module> 7 print 2 + 'abc' 8 TypeError: unsupported operand type(s) for +: 'int' and 'str' Friday, February 18, 2011
74. Type Coercion 1 print 5 * 1.0 2 print 2 ** 100 3 print 2 * 'abc' 4 print 2 + 'abc' 1 $ python type_coercion.py 2 5.0 3 1267650600228229401496703205376 4 abcabc 5 Traceback (most recent call last): 6 File ".../type_coercion.py", line 4, in <module> 7 print 2 + 'abc' 8 TypeError: unsupported operand type(s) for +: 'int' and 'str' Friday, February 18, 2011
75. Type Coercion 1 print 5 * 1.0 2 print 2 ** 100 3 print 2 * 'abc' 4 print 2 + 'abc' 1 $ python type_coercion.py 2 5.0 3 1267650600228229401496703205376 4 abcabc 5 Traceback (most recent call last): 6 File ".../type_coercion.py", line 4, in <module> 7 print 2 + 'abc' 8 TypeError: unsupported operand type(s) for +: 'int' and 'str' Friday, February 18, 2011
76. There should be one – and preferably only one – way to do it. • Eliminate redundancy • Easier to learn • Easier to remember Friday, February 18, 2011
77. Index API 1 a = [ 1, 2, 3 ] 2 print a[0] 3 4 a = (1, 2, 3) 5 print a[0] 6 7 a = 'abc' 8 print a[0] 9 10 a = {0:'zero value', 11 1:'one value', 12 } 13 print a[0] $ python index_api.py 1 1 a zero value Friday, February 18, 2011
78. Although that way may not be obvious at first unless you’re Dutch. • GUI • GTK • KDE • Cocoa • MS Windows • Tk • wxPython • Web • Django • AppEngine • Pyramid • Flask • TurboGears • Pecan Friday, February 18, 2011
79. Now is better than never. • ctypes • Jython • IronPython • Python 2 vs. Python 3 Friday, February 18, 2011
80. Although never is often better than right now. • Language moratorium • Not everything goes into stdlib any more Friday, February 18, 2011
81. If the implementation is hard to explain, it’s a bad idea. Python Enhancement Proposals Friday, February 18, 2011
82. If the implementation is easy to explain, it may be a good idea. Friday, February 18, 2011
83. Namespaces are one honking great idea – let’s do more of those! Closures Friday, February 18, 2011
84. Closures 1 def outer(arg): 2 print 'outer(%s)' % arg 3 4 def inner(val): 5 print 'inner(%s) (arg=%s)' % (val, arg) 6 return val * arg 7 8 return inner 9 10 print 'Creating thrice:' 11 thrice = outer(3) 12 13 print '\nCalling thrice:' 14 print thrice(3) 15 print thrice('a') Friday, February 18, 2011
85. Closures 1 def outer(arg): 2 print 'outer(%s)' % arg 3 4 def inner(val): 5 print 'inner(%s) (arg=%s)' % (val, arg) 6 return val * arg 7 8 return inner 9 10 print 'Creating thrice:' 11 thrice = outer(3) 12 13 print '\nCalling thrice:' 14 print thrice(3) 15 print thrice('a') $ python closure.py Creating thrice: outer(3) Calling thrice: inner(3) (arg=3) 9 inner(a) (arg=3) aaa Friday, February 18, 2011
86. References • http://docs.python.org/ • http://www.doughellmann.com/ PyMOTW/ • Learning Python by Mark Lutz • Python Essential Reference by David Beazley • The Python Standard Library by Example by Doug Hellmann • http://us.pycon.org/ Friday, February 18, 2011
87. Questions? Friday, February 18, 2011
88. Image Credits 1. http://www.gaialandscapedesignbackgrounds.net/landscape_design_architecture_background_Zen_Garden_chan3.htm 3. http://www.flickr.com/photos/grabadonut/539151245/sizes/l/in/photostream/ 13. http://www.flickr.com/photos/tobascodagama/3106398602/ 17. http://www.flickr.com/photos/benandliz/11065336/ 21 & 22. http://scipy.org 24. http://www.otherlandtoys.co.uk/russian-matryoshka-nesting-dolls-pieces-p-2126.html 32. http://www.dandelionsummers.com/html/building_block.html 36. http://www.flickr.com/photos/photoinference/2494576240/in/faves-40068198@N04/ 47. http://www.flickr.com/photos/smithsonian/3112472619/in/faves-40068198@N04/ 54. http://www.flickr.com/photos/mherring/3722272868/sizes/l/in/photostream/ 57. http://www.webstaurantstore.com/9-3-4-x-4-1-2-unbleached-natural-coffee-filter-12-cup-1000-cs/121CF12U.html 59. http://brainstorm-services.com/wcu-lit/ambiguity.html 66. http://commons.wikimedia.org/wiki/File:Dutch_windmill.jpg 67. http://www.epicpm.org/epic-blogging 68. http://www.skyscanner.net/news/articles/2009/09/002990-travel-tip-10-get-on-last-and-learn-the-art-of-patience.html 69. http://gizmodo.com/5015735/the-top-10-rube-goldberg-machines-featured-on-film 71. http://www.nutricaplabs.com/capsule-manufacturer.aspx 75. http://wmltech.wordpress.com/2006/12/09/got-questions/ Friday, February 18, 2011