Software Design Complexity and Error Tracing in Python
Interpreting Exceptions
UW CSE 160
Spring 2015
download examples from the calendar
1
There are two ways of constructing a software
design: One way is to make it
so simple that
there are obviously no deficiencies
, and the
other way is to make it
so complicated that
there are no obvious deficiencies
.
Hoare
2
def
friends
(graph, user):
"""Returns a set of the friends of the given user, in
the given graph."""
return
set(graph.neighbors(user))
def
friends_of_friends
(graph, user):
"""Returns a set of friends of friends of the given
user, in the given graph. The result does not include the
user nor their friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friends = friends(graph, user)
fof = fof | friend
g = (fof – f)
g.remove(user)
return
g
3
Traceback (most recent call last):
File "nx_error.py", line 41, in <module>
print friends_of_friends(rj, myval)
File "nx_error.py", line 30, in friends_of_friends
f = friends(graph, user)
File "nx_error.py", line 25, in friends
return set(graph.neighbors(user))#
File "/Library/Frameworks/…/graph.py", line 978, in neighbors
return list(self.adj[n])
myval=["Mercutio"]
friends_of_friends(rj, myval)
see nx_error.py
4
Traceback (most recent call last):
File "nx_error.py", line 41, in <module>
print friends_of_friends(rj, myval)
File
"nx_error.py"
,
line 30
, in
friends_of_friends
f = friends(graph, user)
File "nx_error.py", line 25, in friends
return set(graph.neighbors(user))#
File "/Library/Frameworks/…/graph.py", line 978, in neighbors
return list(self.adj[n])
see nx_error.py
5
Traceback (most recent call last):
File "nx_error.py", line 41, in <module>
print friends_of_friends(rj, myval)
File "nx_error.py", line 30, in friends_of_friends
f = friends(graph, user)
File "nx_error.py", line 25, in friends
return set(graph.neighbors(user))#
File "/Library/Frameworks/…/graph.py", line 978, in neighbors
return list(self.adj[n])
How many stack frames are referenced?
Where did the error actually get noticed?
Where was the original cause of the problem?
myval=["Mercutio"]
friends_of_friends(rj, myval)
see nx_error.py
6
# assume rj was defined previously and correctly
def
friends
(graph, user):
"""Returns the set of friends of user in graph"""
return
set(graph.neighbors(user))
friends = friends(rj, "Mercutio")
friends
friends = friends(rj, "Juliet")
friends
What will be the output?
see name_conflict.py
7
def
friends_of_friends
(graph, user):
"""Returns a set of friends of friends of the given
user, in the given graph. The result does not include the
user nor their friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friends = friends(graph, user)
# name conflict
fof = fof | friend
g = (fof – f)
g.remove(user)
return
g
Same root cause problem,
very different message
see name_conflict2.py
8
def
friends
(graph, user):
"""Returns the set of friends of user in graph"""
return
set(graph.neighbors(user))
friends = friends(rj,
"Mercutio"
)
# name conflict
friends
def
friends_of_friends
(graph, user):
"""Returns a set of friends of friends of the given
user, in the given graph. The result does not include the
user nor their friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friend = friends(graph, user)
fof = fof | friend
g = (fof – f)
g.remove(user)
return
g
friends_of_friends(rj,
“Mecutio”
)
see name_conflict3.py
9
# Two errors -- which is thrown first?
x
# undefined variable
"x"
# bad indentation
Python performs a
syntax check
of your
code before it executes anything.
see syntax_error.py
10
def
friends_of_friends(graph, user):
"""Returns a set of friends of friends of the given user, in
the given graph. The result does not include the user nor their
friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friend = friends(graph, user)
fof = fof | friend
fof = fof.remove(user)
g = (fof - f)
return
g
Traceback (most recent call last):
File "none_error.py", line 21, in <module>
friends_of_friends(g, "Mercutio")
File "none_error.py", line 13, in friends_of_friends
fof = fof | friend
TypeError: unsupported operand type(s) for |: 'NoneType' and 'set'
see none_error.py
11
def
friends_of_friends
(graph, user):
"""Returns a set of friends of friends of the given user, in
the given graph. The result does not include the user nor their
friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friend = friends(graph, user)
fof = fof | friend
g = (fof - f) – user
return
g
Traceback (most recent call last):
File "type_error.py", line 37, in <module>
friends_of_friends(rj, "Mercutio")
File "type_error.py", line 34, in friends_of_friends
g = (fof - f) - user
TypeError: unsupported operand type(s) for -: 'set' and 'str'
see type_error.py
12
def
friends_of_friends(graph, user):
"""Returns a set of friends of friends of the given user, in
the given graph. The result does not include the user nor their
friends """
fof = set()
f = friends(graph, user)
for
fren
in
f:
friend = friends(graph, user)
fof = fof | friend
f.add(set([user]))
g = (fof - f)
return
g
Traceback (most recent call last):
File "unhashable_type.py", line 21, in <module>
friends_of_friends(g, "Mercutio")
File "unhashable_type.py", line 14, in friends_of_friends
f.add([user])
TypeError: unhashable type: ’set'
see unhashable_type.py
13
Explore the concepts of software design complexity through quotes by Hoare, and traceback errors in Python code showcasing the identification of stack frames, error detection points, and original problem causes, emphasizing the importance of simplicity in design.
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Presentation Transcript
Interpreting Exceptions UW CSE 160 Spring 2015 download examples from the calendar 1
There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. Hoare 2
def friends(graph, user): """Returns a set of the friends of the given user, in the given graph.""" return set(graph.neighbors(user)) def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friends = friends(graph, user) fof = fof | friend g = (fof f) g.remove(user) return g 3
myval=["Mercutio"] print friends_of_friends(rj, myval) Traceback (most recent call last): File "nx_error.py", line 41, in <module> print friends_of_friends(rj, myval) File "nx_error.py", line 30, in friends_of_friends f = friends(graph, user) File "nx_error.py", line 25, in friends return set(graph.neighbors(user))# File "/Library/Frameworks/ /graph.py", line 978, in neighbors return list(self.adj[n]) see nx_error.py 4
Traceback: a description of the stack. Each stack frame in the stack is described by a filename line number function name Further, the line itself is printed for convenience Traceback (most recent call last): File "nx_error.py", line 41, in <module> print friends_of_friends(rj, myval) File "nx_error.py", line 30, in friends_of_friends f = friends(graph, user) File "nx_error.py", line 25, in friends return set(graph.neighbors(user))# File "/Library/Frameworks/ /graph.py", line 978, in neighbors return list(self.adj[n]) see nx_error.py 5
myval=["Mercutio"] print friends_of_friends(rj, myval) Traceback (most recent call last): File "nx_error.py", line 41, in <module> print friends_of_friends(rj, myval) File "nx_error.py", line 30, in friends_of_friends f = friends(graph, user) File "nx_error.py", line 25, in friends return set(graph.neighbors(user))# File "/Library/Frameworks/ /graph.py", line 978, in neighbors return list(self.adj[n]) How many stack frames are referenced? Where did the error actually get noticed? Where was the original cause of the problem? see nx_error.py 6
# assume rj was defined previously and correctly def friends(graph, user): """Returns the set of friends of user in graph""" return set(graph.neighbors(user)) friends = friends(rj, "Mercutio") print friends friends = friends(rj, "Juliet") print friends What will be the output? see name_conflict.py 7
def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friends = friends(graph, user) # name conflict fof = fof | friend g = (fof f) g.remove(user) return g Same root cause problem, very different message see name_conflict2.py 8
def friends(graph, user): """Returns the set of friends of user in graph""" return set(graph.neighbors(user)) friends = friends(rj, "Mercutio") # name conflict print friends def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friend = friends(graph, user) fof = fof | friend g = (fof f) g.remove(user) return g print friends_of_friends(rj, Mecutio ) see name_conflict3.py 9
# Two errors -- which is thrown first? print x # undefined variable print "x" # bad indentation Python performs a syntax check of your code before it executes anything. see syntax_error.py 10
def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friend = friends(graph, user) fof = fof | friend fof = fof.remove(user) g = (fof - f) return g Traceback (most recent call last): File "none_error.py", line 21, in <module> friends_of_friends(g, "Mercutio") File "none_error.py", line 13, in friends_of_friends fof = fof | friend TypeError: unsupported operand type(s) for |: 'NoneType' and 'set' see none_error.py 11
def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friend = friends(graph, user) fof = fof | friend g = (fof - f) user return g Traceback (most recent call last): File "type_error.py", line 37, in <module> friends_of_friends(rj, "Mercutio") File "type_error.py", line 34, in friends_of_friends g = (fof - f) - user TypeError: unsupported operand type(s) for -: 'set' and 'str' see type_error.py 12
def friends_of_friends(graph, user): """Returns a set of friends of friends of the given user, in the given graph. The result does not include the user nor their friends """ fof = set() f = friends(graph, user) for fren in f: friend = friends(graph, user) fof = fof | friend f.add(set([user])) g = (fof - f) return g Traceback (most recent call last): File "unhashable_type.py", line 21, in <module> friends_of_friends(g, "Mercutio") File "unhashable_type.py", line 14, in friends_of_friends f.add([user]) TypeError: unhashable type: set' see unhashable_type.py 13
