The document discusses Python functions. It explains that functions allow programmers to define reusable blocks of code to perform tasks or operations. It provides examples of defining functions using def, passing parameters to functions, and how each function call creates a new stack frame. It also discusses how functions can return values and the concept that every function in Python returns something, even if it is None.

1. Python
Functions
Copyright © Software Carpentry 2010
This work is licensed under the Creative Commons Attribution License
See http://software-carpentry.org/license.html for more information.

2. A programming language should not include
everything anyone might ever want
Python Functions

3. A programming language should not include
everything anyone might ever want
Instead, it should make it easy for ppeeooppllee ttoo ccrreeaattee
what they need to solve specific problems
Python Functions

4. A programming language should not include
everything anyone might ever want
Instead, it should make it easy for ppeeooppllee ttoo ccrreeaattee
what they need to solve specific problems
Define functions to create higher-level operations
Python Functions

5. A programming language should not include
everything anyone might ever want
Instead, it should make it easy for ppeeooppllee ttoo ccrreeaattee
what they need to solve specific problems
Define functions to create higher-level operations
"Create a language in which the solution to your
original problem is trivial."
Python Functions

6. Define functions using def
Python Functions

7. Define functions using def
ddddeeeeffff greet():
rrrreeeettttuuuurrrrnnnn 'Good evening, master'
Python Functions

8. Define functions using def
ddddeeeeffff greet():
rrrreeeettttuuuurrrrnnnn 'Good evening, master'
temp = greet()
pppprrrriiiinnnntttt temp
Good evening, master
Python Functions

9. Give them parameters
Python Functions

10. Give them parameters
ddddeeeeffff greet(name):
answer = 'Hello, ' + name
rrrreeeettttuuuurrrrnnnn answer
Python Functions

11. Give them parameters
ddddeeeeffff greet(name):
answer = 'Hello, ' + name
temp
'doctor'
rrrreeeettttuuuurrrrnnnn answer
temp = 'doctor'
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

12. Give them parameters
ddddeeeeffff greet(name):
answer = 'Hello, ' + name
temp
'doctor'
name
rrrreeeettttuuuurrrrnnnn answer
temp = 'doctor'
result = greet(temp)
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

13. Give them parameters
ddddeeeeffff greet(name):
answer = 'Hello, ' + name
temp
'doctor'
'Hello, doctor'
name
answer
rrrreeeettttuuuurrrrnnnn answer
temp = 'doctor'
result = greet(temp)
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

14. Give them parameters
ddddeeeeffff greet(name):
answer = 'Hello, ' + name
temp
'doctor'
'Hello, doctor'
rrrreeeettttuuuurrrrnnnn answer
temp = 'doctor'
result = greet(temp)
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

15. Each function call creates a new stack frame
Python Functions

16. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

17. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
val
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

18. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
c
val
ddddoooouuuubbbblllleeee
result = double(val)
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

19. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
a
c
val
ddddoooouuuubbbblllleeee aaaadddddddd
result = double(val)
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

20. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
11
a
b
c
val
ddddoooouuuubbbblllleeee aaaadddddddd
result = double(val)
pppprrrriiiinnnntttt result
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

21. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
22
c
d
val
ddddoooouuuubbbblllleeee
result = double(val)
pppprrrriiiinnnntttt result
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

22. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
22
val
result = double(val)
pppprrrriiiinnnntttt result
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

23. Each function call creates a new stack frame
ddddeeeeffff add(a):
b = a + 1
rrrreeeettttuuuurrrrnnnn b
ddddeeeeffff double(c):
d = 2 * add(c)
rrrreeeettttuuuurrrrnnnn d
val = 10
10
22
val
result = double(val)
pppprrrriiiinnnntttt result
22
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

24. Only see variables in the current and global frames
Python Functions

25. Only see variables in the current and global frames
Current beats global
Python Functions

26. Only see variables in the current and global frames
Current beats global
ddddddddeeeeeeeeffffffff ggrreeeett((nnaammee))::
temp = 'Hello, ' + name
rrrreeeettttuuuurrrrnnnn temp
temp = 'doctor'
result = greet(temp)
Python Functions

27. Only see variables in the current and global frames
Current beats global
ddddddddeeeeeeeeffffffff ggrreeeett((nnaammee))::
temp = 'Hello, ' + name
rrrreeeettttuuuurrrrnnnn temp
temp = 'doctor'
result = greet(temp) temp
'Hello, doctor'
'doctor'
gggglllloooobbbbaaaallll
ggggrrrreeeeeeeetttt
name
temp
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

28. Only see variables in the current and global frames
Current beats global
ddddddddeeeeeeeeffffffff ggrreeeett((nnaammee))::
temp = 'Hello, ' + name
rrrreeeettttuuuurrrrnnnn temp
temp = 'doctor'
result = greet(temp)
pppprrrriiiinnnntttt result
temp
'Hello, doctor'
'doctor'
gggglllloooobbbbaaaallll
Hello, doctor
result
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

29. Can pass values in and accept results directly
Python Functions

30. Can pass values in and accept results directly
ddddeeeeffff greet(name):
rrrreeeettttuuuurrrrnnnn 'Hello, ' + name
pppprrrriiiinnnntttt greet('doctor')
Python Functions

31. Can pass values in and accept results directly
ddddeeeeffff greet(name):
rrrreeeettttuuuurrrrnnnn 'Hello, ' + name
pppprrrriiiinnnntttt greet('doctor')
_x1_
'doctor'
'Hello, doctor'
name
_x2_
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

32. Can return at any time
Python Functions

33. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
Python Functions

34. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
Python Functions

35. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
pppprrrriiiinnnntttt sign(-9)
-1
Python Functions

36. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
Over-use makes functions
rrrreeeettttuuuurrrrnnnn 1 hard to understand
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
pppprrrriiiinnnntttt sign(-9)
-1
Python Functions

37. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
Over-use makes functions
rrrreeeettttuuuurrrrnnnn 1 hard to understand
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
No prescription possible, but:
1
pppprrrriiiinnnntttt sign(-9)
-1
Python Functions

38. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
Over-use makes functions
rrrreeeettttuuuurrrrnnnn 1 hard to understand
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
No prescription possible, but:
– a few at the beginning
to handle special cases
1
pppprrrriiiinnnntttt sign(-9)
-1
Python Functions

39. Can return at any time
ddddeeeeffff sign(num):
iiiiffff num > 0:
Over-use makes functions
rrrreeeettttuuuurrrrnnnn 1 hard to understand
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
eeeellllsssseeee::::
rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
No prescription possible, but:
– a few at the beginning
to handle special cases
– one at the end for the
1
pppprrrriiiinnnntttt sign(-9)
-1
"general" result
Python Functions

40. Every function returns something
Python Functions

41. Every function returns something
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
# eeeellllsssseeee::::
# rrrreeeettttuuuurrrrnnnn -1
Python Functions

42. Every function returns something
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
# eeeellllsssseeee::::
# rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
Python Functions

43. Every function returns something
ddddeeeeffff sign(num):
iiiiffff num > 0:
rrrreeeettttuuuurrrrnnnn 1
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
# eeeellllsssseeee::::
# rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
pppprrrriiiinnnntttt sign(-9)
None
Python Functions

44. Every function returns something
ddddeeeeffff sign(num):
iiiiffff num > 0:
If the function doesn't return
rrrreeeettttuuuurrrrnnnn 1 a value, Python returns None
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
# eeeellllsssseeee::::
# rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
1
pppprrrriiiinnnntttt sign(-9)
None
Python Functions

45. Every function returns something
ddddeeeeffff sign(num):
iiiiffff num > 0:
If the function doesn't return
rrrreeeettttuuuurrrrnnnn 1 a value, Python returns None
eeeelllliiiiffff num == 0:
rrrreeeettttuuuurrrrnnnn 0
# eeeellllsssseeee::::
# rrrreeeettttuuuurrrrnnnn -1
pppprrrriiiinnnntttt sign(3)
Yet another reason why
commenting out blocks of code
is a bad idea...
1
pppprrrriiiinnnntttt sign(-9)
None
Python Functions

46. Functions and parameters don't have types
Python Functions

47. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
Python Functions

48. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
pppprrrriiiinnnntttt double(2)
4
Python Functions

49. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
pppprrrriiiinnnntttt double(2)
4
pppprrrriiiinnnntttt double('two')
twotwo
Python Functions

50. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
Only use this when the
function's behavior depends
pppprrrriiiinnnntttt double(2)
4
pppprrrriiiinnnntttt double('two')
twotwo
only on properties that all
possible arguments share
Python Functions

51. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
Only use this when the
function's behavior depends
pppprrrriiiinnnntttt double(2)
4
pppprrrriiiinnnntttt double('two')
twotwo
only on properties that all
possible arguments share
iiiiffff type(arg) == int:
...
eeeelllliiiiffff ttttyyyyppppeeee(arg) == str:
...
...
Python Functions

52. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
Only use this when the
function's behavior depends
pppprrrriiiinnnntttt double(2)
4
pppprrrriiiinnnntttt double('two')
twotwo
only on properties that all
possible arguments share
Warning sign iiiiffff type(arg) == int:
...
eeeelllliiiiffff ttttyyyyppppeeee(arg) == str:
...
...
Python Functions

53. Functions and parameters don't have types
ddddeeeeffff double(x):
rrrreeeettttuuuurrrrnnnn 2 * x
Only use this when the
function's behavior depends
pppprrrriiiinnnntttt double(2)
4
pppprrrriiiinnnntttt double('two')
twotwo
only on properties that all
possible arguments share
Warning sign
iiiiffff type(arg) == int:
There's a better
way to do this
...
eeeelllliiiiffff ttttyyyyppppeeee(arg) == str:
...
...
Python Functions

54. Values are copied into parameters
Python Functions

55. Values are copied into parameters
Which means lists are aliased
Python Functions

56. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
Python Functions

57. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
Python Functions

58. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
string_val
'alan'
['alan']
list_val
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

59. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
string_val
'alan'
['alan']
a_string
a_list
list_val
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

60. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
string_val
'alan'
'alanturing'
['alan']
a_string
a_list
list_val
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

61. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
string_val
'alan'
'alanturing'
['alan',
a_string
a_list
list_val 'turing']
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

62. Values are copied into parameters
Which means lists are aliased
ddddddddeeeeeeeeffffffff aappppeennddeerr((aa__ssttrriinngg,, aa__lliisstt))::
a_string += 'turing'
a_list.append('turing')
string_val = 'alan'
list_val = ['alan']
appender(string_val, list_val)
pppprrrriiiinnnntttt string_val
string_val
'alan'
['alan',
alan
pppprrrriiiinnnntttt list_val
['alan', 'turing']
list_val 'turing']
ssssttttaaaacccckkkk vvvvaaaalllluuuueeee
Python Functions

63. Can define default parameter values
Python Functions

64. Can define default parameter values
ddddeeeeffff adjust(value, amount=2.0):
rrrreeeettttuuuurrrrnnnn value * amount
Python Functions

65. Can define default parameter values
ddddeeeeffff adjust(value, amount=2.0):
rrrreeeettttuuuurrrrnnnn value * amount
pppprrrriiiinnnntttt adjust(5)
10
Python Functions

66. Can define default parameter values
ddddeeeeffff adjust(value, amount=2.0):
rrrreeeettttuuuurrrrnnnn value * amount
pppprrrriiiinnnntttt adjust(5)
10
pppprrrriiiinnnntttt adjust(5, 1.001)
5.005
Python Functions

67. More readable than multiple functions
Python Functions

68. More readable than multiple functions
ddddeeeeffff adjust_general(value, amount):
rrrreeeettttuuuurrrrnnnn value * amount
ddddeeeeffff adjust_default(value):
rrrreeeettttuuuurrrrnnnn adjust_general(value, 2.0)
Python Functions

69. Parameters that have defaults must come after
parameters that do not
Python Functions

70. Parameters that have defaults must come after
parameters that do not
ddddeeeeffff triplet(left='venus', middle, right='mars'):
rrrreeeettttuuuurrrrnnnn '%s %s %s' % (left, middle, right)
Python Functions

71. Parameters that have defaults must come after
parameters that do not
ddddeeeeffff triplet(left='venus', middle, right='mars'):
rrrreeeettttuuuurrrrnnnn '%s %s %s' % (left, middle, right)
pppprrrriiiinnnntttt triplet('earth')
venus earth mars
OK so far...
Python Functions

72. Parameters that have defaults must come after
parameters that do not
ddddeeeeffff triplet(left='venus', middle, right='mars'):
rrrreeeettttuuuurrrrnnnn '%s %s %s' % (left, middle, right)
pppprrrriiiinnnntttt triplet('earth')
venus earth mars
pppprrrriiiinnnntttt triplet('pluto', 'earth')
OK so far...
?
Python Functions

73. Parameters that have defaults must come after
parameters that do not
ddddeeeeffff triplet(left='venus', middle, right='mars'):
rrrreeeettttuuuurrrrnnnn '%s %s %s' % (left, middle, right)
pppprrrriiiinnnntttt triplet('earth')
venus earth mars
pppprrrriiiinnnntttt triplet('pluto', 'earth')
OK so far...
?
triplet('pluto', 'earth', 'mars')
Python Functions

74. Parameters that have defaults must come after
parameters that do not
ddddeeeeffff triplet(left='venus', middle, right='mars'):
rrrreeeettttuuuurrrrnnnn '%s %s %s' % (left, middle, right)
pppprrrriiiinnnntttt triplet('earth')
venus earth mars
pppprrrriiiinnnntttt triplet('pluto', 'earth')
OK so far...
?
triplet('pluto', 'earth', 'mars')
triplet('venus', 'pluto', 'earth')
Python Functions

75. "When should I write a function?"
Python Functions

76. "When should I write a function?"
Human short term memory can hold 7± 2 items
Python Functions

77. "When should I write a function?"
Human short term memory can hold 7± 2 items
If someone has to keep more tthhaann aa ddoozzeenn tthhiinnggss
in their mind at once to understand a block of code,
it's too long
Python Functions

78. "When should I write a function?"
Human short term memory can hold 7± 2 items
If someone has to keep more tthhaann aa ddoozzeenn tthhiinnggss
in their mind at once to understand a block of code,
it's too long
Break it into comprehensible pieces with functions
Python Functions

79. "When should I write a function?"
Human short term memory can hold 7± 2 items
If someone has to keep more tthhaann aa ddoozzeenn tthhiinnggss
in their mind at once to understand a block of code,
it's too long
Break it into comprehensible pieces with functions
Even if each function is only called once
Python Functions

80. Example
ffffoooorrrr x iiiinnnn range(1, GRID_WIDTH-1):
ffffoooorrrr y iiiinnnn range(1, GRID_HEIGHT-1):
iiiiffff (density[x-1][y] > density_threshold) or
(density[x+1][y] > density_threshold):
iiiiffff (flow[x][y-1] < flow_threshold) or
(flow[x][y+1] < flow_threshold):
temp = (density[x-1][y] + density[x+1][y]) / 2
iiiiffff abs(temp - density[x][y]) > update_threshold:
density[x][y] = temp
Python Functions

81. Refactoring #1: grid interior
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff (density[x-1][y] > density_threshold) or
(density[x+1][y] > density_threshold):
iiiiffff (flow[x][y-1] > flow_threshold) or
(flow[x][y+1] > flow_threshold):
temp = (density[x-1][y] + density[x+1][y]) / 2
iiiiffff abs(temp - density[x][y]) > update_threshold:
density[x][y] = temp
Python Functions

82. Refactoring #2: tests on X and Y axes
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff density_exceeds(density, x, y, density_threshold):
iiiiffff flow_exceeds(flow, x, y, flow_threshold):
temp = (density[x-1][y] + density[x+1][y]) / 2
iiiiffff abs(temp - density[x][y]) > tolerance:
density[x][y] = temp
Python Functions

83. Refactoring #3: update rule
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff density_exceeds(density, x, y, density_threshold):
iiiiffff flow_exceeds(flow, x, y, flow_threshold):
update_on_tolerance(density, x, y, tolerance)
Python Functions

84. Refactoring #3: update rule
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff density_exceeds(density, x, y, density_threshold):
iiiiffff flow_exceeds(flow, x, y, flow_threshold):
update_on_tolerance(density, x, y, tolerance)
Good programmers will write this first
Python Functions

85. Refactoring #3: update rule
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff density_exceeds(density, x, y, density_threshold):
iiiiffff flow_exceeds(flow, x, y, flow_threshold):
update_on_tolerance(density, x, y, tolerance)
Good programmers will write this first
Then write the functions it implies
Python Functions

86. Refactoring #3: update rule
ffffoooorrrr x iiiinnnn grid_interior(GRID_WIDTH):
ffffoooorrrr y iiiinnnn grid_interior(GRID_HEIGHT):
iiiiffff density_exceeds(density, x, y, density_threshold):
iiiiffff flow_exceeds(flow, x, y, flow_threshold):
update_on_tolerance(density, x, y, tolerance)
Good programmers will write this first
Then write the functions it implies
Then refactor any overlap
Python Functions

87. created by
Greg Wilson
October 2010
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