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First-Class 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. Python
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First-Class Functions An integer is 32 bits of data...
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to A string is a sequence of bytes representing characters...
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to A string is a sequence of bytes representing characters......that variables can refer to
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to A string is a sequence of bytes representing characters......that variables can refer to A function is a sequence of bytes representing instructions...
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to A string is a sequence of bytes representing characters......that variables can refer to A function is a sequence of bytes representing instructions......and yes, variables can refer to them to
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PythonFirst-Class Functions An integer is 32 bits of data......that variables can refer to A string is a sequence of bytes representing characters......that variables can refer to A function is a sequence of bytes representing instructions......and yes, variables can refer to them to This turns out to be very useful, and very powerful
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PythonFirst-Class Functions What happens when a function is defined
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PythonFirst-Class Functions What happens when a function is defined def threshold(signal): return 1.0 / sum(signal)
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PythonFirst-Class Functions What happens when a function is defined def threshold(signal): return 1.0 / sum(signal) stackvalue threshold global 1001 0110 1100 0001 1001
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PythonFirst-Class Functions What happens when a function is defined def threshold(signal): return 1.0 / sum(signal) stackvalue name threshold global 1001 0110 1100 0001 1001 Not really very different from: name = 'Alan Turing' 'alan turing'
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PythonFirst-Class Functions Can assign that value to another variable
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PythonFirst-Class Functions Can assign that value to another variable def threshold(signal): return 1.0 / sum(signal) stackvalue threshold global 1001 0110 1100 0001 1001
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PythonFirst-Class Functions Can assign that value to another variable def threshold(signal): return 1.0 / sum(signal) t = threshold stackvalue t threshold global 1001 0110 1100 0001 1001
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PythonFirst-Class Functions Can assign that value to another variable def threshold(signal): return 1.0 / sum(signal) t = threshold print t([0.1, 0.4, 0.2]) 1.42857 stackvalue t threshold global 1001 0110 1100 0001 1001
![PythonFirst-Class Functions Can assign that value to another variable def threshold(signal): return 1.0 / sum(signal) t = threshold print t([0.1, 0.4, 0.2]) stackvalue t threshold global](http://images.slideplayer.com/26/8788039/slides/slide_16.jpg "PythonFirst-Class Functions Can assign that value to another variable def threshold(signal): return 1.0 / sum(signal) t = threshold print t([0.1, 0.4, 0.2]) stackvalue t threshold global")
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PythonFirst-Class Functions Can put (a reference to) the function in a list
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PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r stackvalue area circumference global 1001 0110 1100 1001 0110 1100
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PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] stackvalue funcs area circumference global 1001 0110 1100 1001 0110 1100
![PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] stackvalue funcs area circumference global](http://images.slideplayer.com/26/8788039/slides/slide_19.jpg "PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] stackvalue funcs area circumference global")
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PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) stackvalue funcs area circumference global 1001 0110 1100 1001 0110 1100
![PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) stackvalue funcs area circumference global](http://images.slideplayer.com/26/8788039/slides/slide_20.jpg "PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) stackvalue funcs area circumference global")
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PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) 3.14159 6.28318 stackvalue funcs area circumference global 1001 0110 1100 1001 0110 1100
![PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) stackvalue funcs area circumference global](http://images.slideplayer.com/26/8788039/slides/slide_21.jpg "PythonFirst-Class Functions Can put (a reference to) the function in a list def area(r): return PI * r * r def circumference(r): return 2 * PI * r funcs = [area, circumference] for f in funcs: print f(1.0) stackvalue funcs area circumference global")
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PythonFirst-Class Functions Can pass (a reference to) the function into a function
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PythonFirst-Class Functions def call_it(func, value): return func(value) Can pass (a reference to) the function into a function
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PythonFirst-Class Functions def call_it(func, value): return func(value) print call_it(area, 1.0) 3.14159 Can pass (a reference to) the function into a function
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PythonFirst-Class Functions def call_it(func, value): return func(value) print call_it(area, 1.0) 3.14159 print call_it(circumference, 1.0) 6.28318 Can pass (a reference to) the function into a function
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PythonFirst-Class Functions Can now write functions of functions
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PythonFirst-Class Functions Can now write functions of functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result
![PythonFirst-Class Functions Can now write functions of functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result](http://images.slideplayer.com/26/8788039/slides/slide_27.jpg "PythonFirst-Class Functions Can now write functions of functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result")
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PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0])
![PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0])](http://images.slideplayer.com/26/8788039/slides/slide_28.jpg "PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0])")
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PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [3.14159, 12.56636, 28.27431]
![PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ]](http://images.slideplayer.com/26/8788039/slides/slide_29.jpg "PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ]")
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PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [3.14159, 12.56636, 28.27431] def slim(text): return text[1:-1]
![PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ] def slim(text): return text[1:-1]](http://images.slideplayer.com/26/8788039/slides/slide_30.jpg "PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ] def slim(text): return text[1:-1]")
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PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [3.14159, 12.56636, 28.27431] def slim(text): return text[1:-1] print do_all(slim, ['abc', 'defgh']) b efg
![PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ] def slim(text): return text[1:-1] print do_all(slim, [ abc , defgh ]) b efg](http://images.slideplayer.com/26/8788039/slides/slide_31.jpg "PythonFirst-Class Functions def do_all(func, values): result = [] for v in values: temp = func(v) result.append(temp) return result Can now write functions of functions print do_all(area, [1.0, 2.0, 3.0]) [ , , ] def slim(text): return text[1:-1] print do_all(slim, [ abc , defgh ]) b efg")
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PythonFirst-Class Functions Higher-order functions allow re-use of control flow
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PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Higher-order functions allow re-use of control flow
![PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Higher-order functions allow re-use of control flow](http://images.slideplayer.com/26/8788039/slides/slide_33.jpg "PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Higher-order functions allow re-use of control flow")
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PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y Higher-order functions allow re-use of control flow
![PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y Higher-order functions allow re-use of control flow](http://images.slideplayer.com/26/8788039/slides/slide_34.jpg "PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y Higher-order functions allow re-use of control flow")
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PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 Higher-order functions allow re-use of control flow
![PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 Higher-order functions allow re-use of control flow](http://images.slideplayer.com/26/8788039/slides/slide_35.jpg "PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 Higher-order functions allow re-use of control flow")
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PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 print combine_values(mul, [1, 3, 5]) 15 Higher-order functions allow re-use of control flow
![PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 print combine_values(mul, [1, 3, 5]) 15 Higher-order functions allow re-use of control flow](http://images.slideplayer.com/26/8788039/slides/slide_36.jpg "PythonFirst-Class Functions def combine_values(func, values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current def add(x, y): return x + y def mul(x, y): return x * y print combine_values(add, [1, 3, 5]) 9 print combine_values(mul, [1, 3, 5]) 15 Higher-order functions allow re-use of control flow")
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PythonFirst-Class Functions Without higher order functions
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PythonFirst-Class Functions Without higher order functions op_1op_2op_3 data_structure_Ado_1Ado_2Ado_3A data_structure_Bdo_1Bdo_2Bdo_3B data_structure_Cdo_1Cdo_2Cdo_3C
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PythonFirst-Class Functions Without higher order functions op_1op_2op_3 data_structure_Ado_1Ado_2Ado_3A data_structure_Bdo_1Bdo_2Bdo_3B data_structure_Cdo_1Cdo_2Cdo_3C total: 9
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PythonFirst-Class Functions Without higher order functions op_1op_2op_3 data_structure_Ado_1Ado_2Ado_3A data_structure_Bdo_1Bdo_2Bdo_3B data_structure_Cdo_1Cdo_2Cdo_3C With higher order functions total: 9
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PythonFirst-Class Functions Without higher order functions op_1op_2op_3 data_structure_Ado_1Ado_2Ado_3A data_structure_Bdo_1Bdo_2Bdo_3B data_structure_Cdo_1Cdo_2Cdo_3C With higher order functions op_1op_2op_3 operate_on_A operate_on_B operate_on_C total: 9
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PythonFirst-Class Functions Without higher order functions op_1op_2op_3 data_structure_Ado_1Ado_2Ado_3A data_structure_Bdo_1Bdo_2Bdo_3B data_structure_Cdo_1Cdo_2Cdo_3C With higher order functions op_1op_2op_3 operate_on_A operate_on_B operate_on_C total: 9 total: 6
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PythonFirst-Class Functions Must need to know something about the function in order to call it
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments def add_all(*args): total = 0 for a in args: total += a return total
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments def add_all(*args): total = 0 for a in args: total += a return total
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments def add_all(*args): total = 0 for a in args: total += a return total print add_all() 0
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PythonFirst-Class Functions Must need to know something about the function in order to call it Like number of arguments def add_all(*args): total = 0 for a in args: total += a return total print add_all() 0 print add_all(1, 2, 3) 6
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PythonFirst-Class Functions Combine with "regular" parameters
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PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with "regular" parameters
![PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with regular parameters](http://images.slideplayer.com/26/8788039/slides/slide_51.jpg "PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with regular parameters")
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PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with "regular" parameters
![PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with regular parameters](http://images.slideplayer.com/26/8788039/slides/slide_52.jpg "PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current Combine with regular parameters")
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PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with "regular" parameters
![PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with regular parameters](http://images.slideplayer.com/26/8788039/slides/slide_53.jpg "PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with regular parameters")
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PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with "regular" parameters What does combine_values(add) do?
![PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with regular parameters What does combine_values(add) do](http://images.slideplayer.com/26/8788039/slides/slide_54.jpg "PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with regular parameters What does combine_values(add) do")
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PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with "regular" parameters What does combine_values(add) do? What should it do?
![PythonFirst-Class Functions def combine_values(func, *values): current = values[0] for i in range(1, len(values)): current = func(current, v) return current print combine_values(add, 1, 3, 5) 9 Combine with regular parameters What does combine_values(add) do.](http://images.slideplayer.com/26/8788039/slides/slide_55.jpg "What should it do .")
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S)apply F to each element of S
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2]
![PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2]](http://images.slideplayer.com/26/8788039/slides/slide_59.jpg "PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2]")
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2]
![PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2]](http://images.slideplayer.com/26/8788039/slides/slide_60.jpg "PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2]")
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PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2] def add(x, y): return x+y print reduce(add, [-3, -2, 0, 1, 2]) -2
![PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2] def add(x, y): return x+y print reduce(add, [-3, -2, 0, 1, 2]) -2](http://images.slideplayer.com/26/8788039/slides/slide_61.jpg "PythonFirst-Class Functions filter(F, S) select elements of S for which F is True map(F, S) apply F to each element of S reduce(F, S) use F to combine all elements of S def positive(x): return x >= 0 print filter(positive, [-3, -2, 0, 1, 2]) [0, 1, 2] def negate(x): return -x print map(negate, [-3, -2, 0, 1, 2]) [3, 2, 0, -1, -2] def add(x, y): return x+y print reduce(add, [-3, -2, 0, 1, 2]) -2")
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PythonFirst-Class Functions What is programming?
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions figure out what the pattern is
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions figure out what the pattern is write it down as clearly as possible
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions figure out what the pattern is write it down as clearly as possible build more patterns on top of it
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions figure out what the pattern is write it down as clearly as possible build more patterns on top of it But limits on short-term memory still apply
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PythonFirst-Class Functions What is programming? Novice:writing instructions for the computer Expert:creating and combining abstractions figure out what the pattern is write it down as clearly as possible build more patterns on top of it But limits on short-term memory still apply Hard to understand what meta-meta-functions actually do
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October 2010 created by Greg Wilson Copyright © Software Carpentry 2010 This work is licensed under the Creative Commons Attribution License See http://software-carpentry.org/license.html for more information.
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