1. Принципы и практики
разработки ПО
Лекция 2

2. SOLID principles
S SRP
O OCP
L LSP
I ISP
D DIP
Single Responsibility Principle
Open-Close Principle
Liskov Substitution Principle
Interface Segregation Principle
Dependency Inversion Principle

3. class ILampSwitcher:
def switch(self, on_off):
pass
def is_on(self):
return self.light_on
class DaylightLamp(ILampSwitcher):
pass
class TableLamp(ILampSwitcher):
pass
Liskov Substitution Principle (LSP)
ILampSwitcher
TableLampDaylightLamp
+switch(on_off: bool)
+is_on(): bool

4. def turn_all_on(lamps):
for lamp in lamps:
lamp.switch(True)
l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
Liskov Substitution Principle (LSP)
TableLampDaylightLamp
ILampSwitcher
+switch(on_off: bool)
+is_on(): bool

5. def turn_all_on(lamps):
for lamp in lamps:
lamp.switch(True)
l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
turn_all_on([l1, l2]) # OK
turn_all_on([l3, l4]) # Exception
Liskov Substitution Principle (LSP)
TableLampDaylightLamp
ILampSwitcher
+switch(on_off: bool)
+is_on(): bool

6. def turn_all_on(lamps):
for lamp in lamps:
lamp.switch(True)
l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
turn_all_on([l1, l2]) # OK
turn_all_on([l3, l4]) # Exception
Liskov Substitution Principle (LSP)
class DaylightLamp(ILampSwitcher):
def switch(self, on_off):
self.light_on = on_off

7. def turn_all_on(lamps):
for lamp in lamps:
lamp.switch(True)
l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
turn_all_on([l1, l2]) # OK
turn_all_on([l3, l4]) # Exception
Liskov Substitution Principle (LSP)
class DaylightLamp(ILampSwitcher):
def switch(self, on_off):
self.light_on = on_off
class TableLamp(ILampSwitcher):
def switch(self, on_off):
# debug
f = open("c:v_pupkintmp.txt", 'w')
f.write("Lamp state: " + str(self.is_on()))
self.light_on = on_off

8. l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
turn_all_on([l1, l2]) # OK
turn_all_on([l1, l2]) # OK
turn_all_on([l3, l4]) # OK
turn_all_on([l3, l4]) # Exception
Liskov Substitution Principle (LSP)
class DaylightLamp(ILampSwitcher):
def switch(self, on_off):
...
class TableLamp(ILampSwitcher):
def switch(self, on_off):
...

9. l1 = DaylightLamp()
l2 = DaylightLamp()
l3 = TableLamp()
l4 = TableLamp()
turn_all_on([l1, l2]) # OK
turn_all_on([l1, l2]) # OK
turn_all_on([l3, l4]) # OK
turn_all_on([l3, l4]) # Exception
Liskov Substitution Principle (LSP)
class DaylightLamp(ILampSwitcher):
def switch(self, on_off):
self.light_on = on_off
class TableLamp(ILampSwitcher):
def switch(self, on_off):
if self.light_on and on_off:
raise Exception("Already on.")
if not self.light_on and not on_off:
raise Exception("Already off.")
self.light_on = on_off

10. class ILampSwitcher:
# Switches on or off.
# No throw of exceptions.
def switch(self, on_off):
pass
# Returns is lamp on.
# No throw of exceptions.
def is_on(self):
return self.light_on
# Blinks every interval (ms) if turned on.
# Throws NotSupportedException if lamp can't do this.
def blink(interval):
pass
Keeping contracts == obey LSP
class DaylightLamp(ILampSwitcher):
def switch(self, on_off):
self.light_on = on_off
def blink(interval):
raise NotSupportedException()

11. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switch_all(self, on_off: bool):
pass
Contracts, interface consistency and LSP

12. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switch_all(self, on_off: bool):
pass
class MultiLamp(IMultiLampSwitcher):
def __init__(self, lamps_count):
self.lamps_count = lamps_count
self.lamps = [False] * lamps_count
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
self.lamps[idx] = on_off
Contracts, interface consistency and LSP

13. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switch_all(self, on_off: bool):
pass
class MultiLamp(IMultiLampSwitcher):
def __init__(self, lamps_count):
self.lamps_count = lamps_count
self.lamps = [False] * lamps_count
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
self.lamps[idx] = on_off
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def __init__(self):
super(SmartOfficeLamp, self).__init__(3)
self.switching_times = [0] * 3
def switch(self, idx, on_off: bool):
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
super(SmartOfficeLamp, self).switch_all(on_off)

14. Contracts, interface consistency and LSP
IMultiLampSwitcher
MultiLamp
+switch(idx:int, on_off: bool)
+switch_all(on_off:bool)
SmartOfficeLamp
+switch(idx:int, on_off: bool)
+switch_all(on_off:bool)
+switch(idx:int, on_off: bool)
+switch_all(on_off:bool)

15. class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
self.lamps[idx] = on_off
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
super(SmartOfficeLamp, self).switch_all(on_off)

16. class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
self.lamps[idx] = on_off
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch_all(on_off)

17. class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
self.lamps[idx] = on_off
l = SmartOfficeLamp()
print(l.lamps) # [False, False, False]
print(l.switching_times) # [0, 0, 0]
l.switch_all(True)
print(l.lamps) # [True, True, True]
print(l.switching_times) # [1, 1, 1]
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch_all(on_off)

18. class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
# self.lamps[idx] = on_off
self.switch(idx, on_off)
l = SmartOfficeLamp()
print(l.lamps) # [False, False, False]
print(l.switching_times) # [0, 0, 0]
l.switch_all(True)
print(l.lamps)
print(l.switching_times)
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch_all(on_off)

19. class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
# self.lamps[idx] = on_off
self.switch(idx, on_off)
l = SmartOfficeLamp()
print(l.lamps) # [False, False, False]
print(l.switching_times) # [0, 0, 0]
l.switch_all(True)
print(l.lamps) # [True, True, True]
print(l.switching_times) # [2, 2, 2]
Contracts, interface consistency and LSP
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch(idx, on_off)
def switch_all(self, on_off: bool):
for idx in range(self.lamps_count):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch_all(on_off)

20. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switchers_count(self):
pass
@staticmethod
def switch_all(multi_lamp_switcher, on_off):
cnt = multi_lamp_switcher.switchers_count()
for idx in range(cnt):
multi_lamp_switcher.switch(idx, on_off)
Contracts, interface consistency and LSP

21. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switchers_count(self):
pass
@staticmethod
def switch_all(multi_lamp_switcher, on_off):
cnt = multi_lamp_switcher.switchers_count()
for idx in range(cnt):
multi_lamp_switcher.switch(idx, on_off)
Contracts, interface consistency and LSP
class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switchers_count(self):
return self.lamps_count

22. class IMultiLampSwitcher:
def switch(self, idx, on_off: bool):
pass
def switchers_count(self):
pass
@staticmethod
def switch_all(multi_lamp_switcher, on_off):
cnt = multi_lamp_switcher.switchers_count()
for idx in range(cnt):
multi_lamp_switcher.switch(idx, on_off)
Contracts, interface consistency and LSP
class MultiLamp(IMultiLampSwitcher):
def switch(self, idx, on_off: bool):
self.lamps[idx] = on_off
def switchers_count(self):
return self.lamps_count
class SmartOfficeLamp(MultiLamp):
def switch(self, idx, on_off: bool):
if on_off != self.lamps[idx]:
self.switching_times[idx] += 1
super(SmartOfficeLamp, self).switch(idx, on_off)
l = SmartOfficeLamp()
IMultiLampSwitcher.switch_all(l, True)

23. The end