Re: [Tutor] Return T/F vs print T/F
On 2/4/2012 11:53 AM, Steven D'Aprano wrote: [snip] In the interactive interpreter, as a convenience, the result of each line is automatically printed for you: Actually the interpreter prints the result of each /statement /that IS an /expression/. >>> 2 2 >>> a = 3 >>> a 3 IOW if the line is blank, start with # or is a statement the interpreter does not print anything (unless it is a print statement). For a messy example: >>> if 1:3;a=4;a ... 3 4 -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Return T/F vs print T/F
On Sat, Feb 4, 2012 at 11:42 AM, Sivaram Neelakantan wrote: > On Sat, Feb 04 2012,bob gailer wrote: > >> On 2/4/2012 9:38 AM, Sivaram Neelakantan wrote: >>> While trying out code, I have trouble following the difference between >>> >>> return True vs print True and the same with False. If I use return >>> for the True/False statements, nothing gets printed. Why? >> >> Why did you expect something to be printed? > > err...return sends something back as in True or False? Yes, it returns it to the caller. It doesn't print it. When using the interactive mode, the program that creates that mode prints the return. When you are using it your program, the caller decides what to do. The flip side is that printing a value does NOT return it. -- Brett Ritter / SwiftOne swift...@swiftone.org ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Return T/F vs print T/F
Sivaram Neelakantan wrote: def palin(text): if first(text) == last(text): # print first(text), last(text), middle(text), len(middle(text)) if len(middle(text)) == 0: print True else: palin(middle(text)) else: print False Every branch of the function must include a return, or Python will just return None by default. You have three branches. Two of them print a flag. It is easy enough to fix them by changing print to return. The third branch has no return. It needs one. -- Steven ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Return T/F vs print T/F
Sivaram Neelakantan wrote:
While trying out code, I have trouble following the difference between
return True vs print True and the same with False. If I use return
for the True/False statements, nothing gets printed. Why?
Probably because you aren't printing anything. Python can't read your mind and
know what you want printed and what you don't want printed, you have to tell
it what to print.
It is not clear how you are "trying out code". Are you running code as a
script? Using IDLE or iPython? Using the standard interactive interpreter? The
environment will make a difference in the behaviour.
In the interactive interpreter, as a convenience, the result of each line is
automatically printed for you:
>>> 1+3
4
>>> len("hello world")
11
but this is only in the interactive environment. In a script, nothing is
printed unless you call print.
Functions should have a return result -- the value they calculate. You can
then store the value in a variable for later use:
>>> length = len("hello world") # store the value
>>> print "The length is", length # and use it later
The length is 11
The print command does not return a value, it just prints the argument. If you
use print in the function, you cannot capture the result and use it in
additional calculations.
When writing your own functions, you should always aim for this same
behaviour: use return inside the function, print outside.
And if I add a print before the function call I get an output like
True
None
I can't see any possible way your code will give output including ">>>". Would
you care to explain more carefully what you mean?
--
Steven
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Re: [Tutor] Return T/F vs print T/F
On Sat, Feb 04 2012,bob gailer wrote: > On 2/4/2012 9:38 AM, Sivaram Neelakantan wrote: >> While trying out code, I have trouble following the difference between >> >> return True vs print True and the same with False. If I use return >> for the True/False statements, nothing gets printed. Why? > > Why did you expect something to be printed? err...return sends something back as in True or False? > > Perhaps you are confused between what happens in the interactive > window vs running a program? Possibly. But I was coding in an Emacs buffer and sending it to the python subprocess from within Emacs. Does that have anything to do with it? > > Python 2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit > (Intel)] on win32 > Type "help", "copyright", "credits" or "license" for more information. def f(): > ... return True > ... f() > True def g(): > ... print True > ... g() > True print f() > True print g() > True > None > > In the interactive window, when you call a function, Python displays > the returned value. When you run a program with a call to a > function, Python does NOT display the returned value. > > A function that does not execute a return will return None; in the > interactive window nothing is displayed. > > Is that sufficient? Right, thanks for this, will check this thing out again. sivaram -- ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Return T/F vs print T/F
On 2/4/2012 9:38 AM, Sivaram Neelakantan wrote: While trying out code, I have trouble following the difference between return True vs print True and the same with False. If I use return for the True/False statements, nothing gets printed. Why? Why did you expect something to be printed? Perhaps you are confused between what happens in the interactive window vs running a program? Python 2.6.5 (r265:79096, Mar 19 2010, 21:48:26) [MSC v.1500 32 bit (Intel)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> def f(): ... return True ... >>> f() True >>> def g(): ... print True ... >>> g() True >>> print f() True >>> print g() True None In the interactive window, when you call a function, Python displays the returned value. When you run a program with a call to a function, Python does NOT display the returned value. A function that does not execute a return will return None; in the interactive window nothing is displayed. Is that sufficient? -- Bob Gailer 919-636-4239 Chapel Hill NC ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] Return T/F vs print T/F
While trying out code, I have trouble following the difference between
return True vs print True and the same with False. If I use return
for the True/False statements, nothing gets printed. Why? And if I
add a print before the function call I get an output like
>>>True
None
--8<---cut here---start->8---
def first(word):
return word[0]
def last(word):
return word[-1]
def middle(word):
return word[1:-1]
def palin(text):
if first(text) == last(text):
# print first(text), last(text), middle(text), len(middle(text))
if len(middle(text)) == 0:
print True
else:
palin(middle(text))
else:
print False
palin("o")
palin("nxon")
palin("nooxooxoon")
print palin("nabban")
--8<---cut here---end--->8---
sivaram
--
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