[Tutor] why do i get None as output
Hello,
I have this programm:
def encapsulate(val, seq):
if type(seq) == type():
return str(val)
if type(seq) == type([]):
return [val]
return (val,)
def insert_in_middle(val, seq):
middle = len(seq)/2
return seq[:middle] + encapsulate(val, seq) + seq[middle:]
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
word2=
teller=0
if type(seq) == type([]):
teller=0
while teller len(seq):
seq[teller]=
teller = teller + 1
elif type(seq) == type(()):
tup2 = list (seq)
while teller tup2.len():
tup2[teller]=
teller = teller + 1
seq = tuple(tup2)
else:
seq =
test = make_empty([1, 2, 3, 4])
print test
But now I get None as output instead of []
Can anyone explain why that happens ?
Roelof
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Re: [Tutor] why do i get None as output
On Mon, Sep 6, 2010 at 8:34 AM, Roelof Wobben rwob...@hotmail.com wrote:
Hello,
I have this programm:
def encapsulate(val, seq):
if type(seq) == type():
return str(val)
if type(seq) == type([]):
return [val]
return (val,)
def insert_in_middle(val, seq):
middle = len(seq)/2
return seq[:middle] + encapsulate(val, seq) + seq[middle:]
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
word2=
teller=0
if type(seq) == type([]):
teller=0
while teller len(seq):
seq[teller]=
teller = teller + 1
elif type(seq) == type(()):
tup2 = list (seq)
while teller tup2.len():
tup2[teller]=
teller = teller + 1
seq = tuple(tup2)
else:
seq =
test = make_empty([1, 2, 3, 4])
print test
But now I get None as output instead of []
Can anyone explain why that happens ?
test = make_empty([1, 2, 3, 4]) makes test equal to the return value
of make_empty. But make_empty does not return anything, and in that
case its return value is made equal to empty. Compare:
def f(x):
x = x + 1
def g(x):
x = x + 1
return x
def h(x):
return x +1
print f(1)
None
print g(1)
2
print h(1)
2
--
André Engels, andreeng...@gmail.com
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Re: [Tutor] why do i get None as output
Roelof Wobben rwob...@hotmail.com wrote def make_empty(seq): word2= teller=0 if type(seq) == type([]): teller=0 while teller len(seq): seq[teller]= teller = teller + 1 elif type(seq) == type(()): tup2 = list (seq) while teller tup2.len(): tup2[teller]= teller = teller + 1 seq = tuple(tup2) else: seq = test = make_empty([1, 2, 3, 4]) But now I get None as output instead of [] Because None is the default return value from a function. If you do not return a value (which you don;t in this case) then Python automatically returns None. You need to return something from your make_empty function. Also, if all you want to do is return an empty version of whatever has been passed in there are much easier ways of doing it! And in fact, a list of empty strings is not the same as an empty list... HTH -- Alan Gauld Author of the Learn to Program web site http://www.alan-g.me.uk/ ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] why do i get None as output
To: tutor@python.org
From: alan.ga...@btinternet.com
Date: Mon, 6 Sep 2010 08:27:31 +0100
Subject: Re: [Tutor] why do i get None as output
Roelof Wobben rwob...@hotmail.com wrote
def make_empty(seq):
word2=
teller=0
if type(seq) == type([]):
teller=0
while teller len(seq):
seq[teller]=
teller = teller + 1
elif type(seq) == type(()):
tup2 = list (seq)
while teller tup2.len():
tup2[teller]=
teller = teller + 1
seq = tuple(tup2)
else:
seq =
test = make_empty([1, 2, 3, 4])
But now I get None as output instead of []
Because None is the default return value from a function.
If you do not return a value (which you don;t in this case) then
Python automatically returns None.
You need to return something from your make_empty function.
Also, if all you want to do is return an empty version of
whatever has been passed in there are much easier
ways of doing it! And in fact, a list of empty strings is
not the same as an empty list...
HTH
--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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Oke,
I put a return seq in the programm and it looks now like this :
def encapsulate(val, seq):
if type(seq) == type():
return str(val)
if type(seq) == type([]):
return [val]
return (val,)
def insert_in_middle(val, seq):
middle = len(seq)/2
return seq[:middle] + encapsulate(val, seq) + seq[middle:]
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
if type(seq) == type([]):
seq = []
elif type(seq) == type(()):
seq=()
else:
seq =
return seq
if __name__ == __main__:
import doctest
doctest.testmod()
This works but I don't think its what the exercise means :
Create a module named seqtools.py. Add the functions encapsulate and
insert_in_middle from the chapter. Add doctests which test that these two
functions work as intended with all three sequence types.
Add each of the following functions to seqtools.py:
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
So i think I have to use encapsulate and insert_in_middle. And I don't use it.
Roelof
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Re: [Tutor] why do i get None as output
On Mon, Sep 6, 2010 at 9:41 AM, Roelof Wobben rwob...@hotmail.com wrote:
To: tutor@python.org
From: alan.ga...@btinternet.com
Date: Mon, 6 Sep 2010 08:27:31 +0100
Subject: Re: [Tutor] why do i get None as output
Roelof Wobben rwob...@hotmail.com wrote
def make_empty(seq):
word2=
teller=0
if type(seq) == type([]):
teller=0
while teller len(seq):
seq[teller]=
teller = teller + 1
elif type(seq) == type(()):
tup2 = list (seq)
while teller tup2.len():
tup2[teller]=
teller = teller + 1
seq = tuple(tup2)
else:
seq =
test = make_empty([1, 2, 3, 4])
But now I get None as output instead of []
Because None is the default return value from a function.
If you do not return a value (which you don;t in this case) then
Python automatically returns None.
You need to return something from your make_empty function.
Also, if all you want to do is return an empty version of
whatever has been passed in there are much easier
ways of doing it! And in fact, a list of empty strings is
not the same as an empty list...
HTH
--
Alan Gauld
Author of the Learn to Program web site
http://www.alan-g.me.uk/
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Oke,
I put a return seq in the programm and it looks now like this :
def encapsulate(val, seq):
if type(seq) == type():
return str(val)
if type(seq) == type([]):
return [val]
return (val,)
def insert_in_middle(val, seq):
middle = len(seq)/2
return seq[:middle] + encapsulate(val, seq) + seq[middle:]
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
if type(seq) == type([]):
seq = []
elif type(seq) == type(()):
seq=()
else:
seq =
return seq
if __name__ == __main__:
import doctest
doctest.testmod()
This works but I don't think its what the exercise means :
Create a module named seqtools.py. Add the functions encapsulate and
insert_in_middle from the chapter. Add doctests which test that these two
functions work as intended with all three sequence types.
Add each of the following functions to seqtools.py:
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
So i think I have to use encapsulate and insert_in_middle. And I don't use
it.
I don't think so. They don't look like the kind of thing that would be
useful for this function. In your example seqtools.py is supposed to
be a (toy example of a) library, a collection of functions to do
things with sequence-like objects to be used by other programs. These
functions in general need not have much to do with eachother, except
that they work on the same type of objects.
--
André Engels, andreeng...@gmail.com
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Re: [Tutor] why do i get None as output
On 06/09/2010 8.34, Roelof Wobben wrote:
Hello,
I have this programm:
...
def make_empty(seq):
make_empty([1, 2, 3, 4])
[]
make_empty(('a', 'b', 'c'))
()
make_empty(No, not me!)
''
word2=
teller=0
if type(seq) == type([]):
teller=0
while teller len(seq):
seq[teller]=
teller = teller + 1
elif type(seq) == type(()):
tup2 = list (seq)
while teller tup2.len():
tup2[teller]=
teller = teller + 1
seq = tuple(tup2)
else:
seq =
test = make_empty([1, 2, 3, 4])
print test
But now I get None as output instead of []
I would add a line like:
return seq
at the end of the make_empty function.
Can anyone explain why that happens ?
I think Python doesn't know what exactly is the value you need to
receive from the make_empty function. That's why I'd make it clear.
Otherwise, you know what happens...
I quote the following from
http://diveintopython.org/getting_to_know_python/declaring_functions.html
In fact, every Python function returns a value; if the function ever
executes a return statement, it will return that value, otherwise it
will return None, the Python null value.
Roelof
Francesco
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