[Tutor] regarding the list problem
Hello I'm a beginner to python. I ran following code and expected [[1, 0], [0, 0], [0, 0]] However unexpected result came up. Anybody who can teach me why and how to solve? Python 3.2.3 (default, May 19 2012, 23:34:41) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> [1] *3 [1, 1, 1] >>> [[0,0]]*3 [[0, 0], [0, 0], [0, 0]] >>> a = [[0,0]]*3 >>> a [[0, 0], [0, 0], [0, 0]] >>> a[0][0] += 1 >>> a [[1, 0], [1, 0], [1, 0]] Kang, Yang Jae Ph.D. Cropgenomics Lab. College of Agriculture and Life Science Seoul National University Korea ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with running perl script that writes to a text file
3n2 Solutions wrote:
> Hello,
>
> I want to automate the following manual process from DOS promp:
>
> c:/scripts/perl>perl fix.pl base.gtx >base.txt
>
> Here is my python script:
>
> path="c:/scripts/perl/"
> subprocess.call(['perl','fix.pl','base.gtx >base.txt',path])
>
> I also tried this alternative:
>
> subprocess.Popen(['perl','fix.pl','base.gtx >base.txt',path]) #same
> result from this method.
>
> The above script generates the base.txt file but has no content in it.
>
> any ideas as to why the resulting text file is empty? Am I using the
> correct python commands to run the above manual process?
I'm surprised that base.txt is generated at all, I'd expect fix.pl to look
for a file named "base.gtx >base.txt" and complain when it doesn't find
that.
I think the following should work:
with open("c:/scripts/perl/base.txt", "w") as f:
subprocess.check_call(
["perl",
"c:/scripts/perl/fix.pl",
"c:/scripts/perl/base.gtx"],
stdout=f)
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Re: [Tutor] help with running perl script that writes to a text file
On Tue, Feb 5, 2013 at 6:44 PM, 3n2 Solutions <3n2soluti...@gmail.com> wrote: > > I want to automate the following manual process from DOS promp: I agree with Peter's answer. I'd just like to add a generally useless and pedantic comment about the habit of saying "DOS prompt". The cmd shell is a Win32 console application, unlike DOS command.com. On 64-bit Windows there isn't even a virtual DOS machine (NTVDM) to run command.com. There, I feel better now. :) ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] regarding the list problem
On Wed, Feb 6, 2013 at 9:48 AM, Kang, Yang Jae wrote: This line: > >>> a = [[0,0]]*3 > creates a list, a, which contains the list object [0, 0] three times. What's crucial to note is that it contains *the same object* three times, not three different objects with the same value. You can verify this yourself, with the id() function: >>> a = [[0,0]] * 3 >>> a [[0, 0], [0, 0], [0, 0]] >>> id(a[0]), id(a[1]), id(a[2]) (41087144, 41087144, 41087144) >>> All three have the same id, therefore all three point to one and the same object. > >>> a > > [[0, 0], [0, 0], [0, 0]] > > >>> a[0][0] += 1 > > >>> a > > [[1, 0], [1, 0], [1, 0]] > It should not be so strange, now, that if you modify a[0], this modification will be reflected in a[1] and a[2] as well, since those are all the same object. Now, this can happen with lists, because they are mutable. If we do the same with integers: >>> a = [1] * 3 >>> a [1, 1, 1] >>> id(a[0]), id(a[1]), id(a[2]) (3779904, 3779904, 3779904) >>> a[0] += 1 >>> a [2, 1, 1] >>> You get the expected behaviour now, even though the list again contained the same object three times. This is because integers are *immutable*, meaning you cannot change them. So this line: >>> a[0] += 1 did not modify the object, but created another integer object, with value 2, and assigned that to a[0]. The conclusion is that you should always be mindful of whether your objects are mutable or not, and you should understand what actually happens when you multiply a list by a constant, to avoid these kinds of problems. In this case, what you wanted to do was create three list objects with value [0, 0], not just the one. You may either generate them with a loop or list comprehension, or simply write the list out in its entirety: >>> a = [[0,0] for i in range(3)] >>> id(a[0]), id(a[1]), id(a[2]) (4070896, 41087984, 41061792) >>> a = [[0, 0], [0, 0], [0, 0]] >>> id(a[0]), id(a[1]), id(a[2]) (41087944, 41087824, 41069624) >>> This way, the lists are actually three different lists and not just the same object three times (as you can see, they have different id's) HTH, Hugo ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] recursive function password check
Hi everyone, trying to write a program that has the user enter a password,
checks if it contains any vowels, and if it does prints ' It is false that
password(whatever the user enters) has no vowels,' and if it has no vowels
prints it is True that password has no vowels...
Here is what I have so far...def password(y): vowels=["a","e","i","o"] if
y[0] in vowels: return False if len(y) ==0: return True
elif(y[len(y)-1] != vowels): return False else: return
password(y[1:len(y)-1])x=input("Enter a password:")print("It is",
password(x),"that",x,"has no vowles")
As of now it just asks for the password, and then prints 'It is False that
password(whatever was entered) has no vowles' for any word I enter. I think
maybe some of my if statement conditions may be being returned to the function,
but then not printing the appropriate one? Can anyone help? Thanks!___
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Re: [Tutor] recursive function password check
On Wed, Feb 6, 2013 at 1:44 PM, Mara Kelly wrote:
> Hi everyone, trying to write a program that has the user enter a password,
> checks if it contains any vowels, and if it does prints ' It is false that
> password(whatever the user enters) has no vowels,' and if it has no vowels
> prints it is True that password has no vowels...
>
> Here is what I have so far...
>
def password(y):
> vowels=["a","e","i","o"]
> if y[0] in vowels:
> return False
> if len(y) ==0:
> return True
> elif(y[len(y)-1] != vowels):
> return False
> else:
> return password(y[1:len(y)-1])
> x=input("Enter a password:")
> print("It is", password(x),"that",x,"has no vowles")
>
>
Okay, it looks to me like you are inspecting the first and last characters
in the string, returning False if some condition is met for each, and
otherwise you chop them off and call recursively on the resulting string.
So here's a question for you: For the first character, you check if y[0]
in vowels. But for the last character, you check if y[len(y) - 1] !=
vowels. Why did you use "in" for the first test, and "!=" for the second?
By the way, here's a related tip: in Python, negative indexes will work
from the back of the sequence. So y[-1] is the last element, y[-2] the
second to last, et cetera.
HTH,
Hugo
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Re: [Tutor] recursive function password check
On Wed, Feb 6, 2013 at 9:44 PM, Mara Kelly wrote:
> Hi everyone, trying to write a program that has the user enter a password,
> checks if it contains any vowels, and if it does prints ' It is false that
> password(whatever the user enters) has no vowels,' and if it has no vowels
> prints it is True that password has no vowels...
>
> Here is what I have so far...
> def password(y):
> vowels=["a","e","i","o"]
> if y[0] in vowels:
> return False
> if len(y) ==0:
> return True
> elif(y[len(y)-1] != vowels):
> return False
> else:
> return password(y[1:len(y)-1])
> x=input("Enter a password:")
> print("It is", password(x),"that",x,"has no vowles")
>
> As of now it just asks for the password, and then prints 'It is False that
> password(whatever was entered) has no vowles' for any word I enter. I think
> maybe some of my if statement conditions may be being returned to the
> function, but then not printing the appropriate one? Can anyone help?
> Thanks!
>
It appears that the issue is from this:
elif(y[len(y)-1] != vowels):
This condition will be true because you are comparing a string with a list.
Thus causing passwrod() returning False.
>
> ___
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>
>
--
Regards,
YeeYaa (Simon Yan)
http://simonyan.fedorapeople.org/
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Re: [Tutor] recursive function password check
Hi Mara,
Several suggestions:
Put the password in a list, then loop each letter to check if it is a vowel
like this
password=[]
vowels=['a','e','i','o','u']#in your message, u is missing, BTW
password=input("Enter a password:")
for p in password:
if p in vowels:
return True #I would use print("the message that you want to
display") though.
else:
return False
And how about error handling? You put
if len(y) ==0:
return True #I would use print("woops! You did not enter
anything.") and add break
Does this password case sensitive? If so, add AEIOU in vowels list.
Good luck!
Noriko
From: Tutor [mailto:tutor-bounces+noriko.tani=tomtom@python.org] On Behalf
Of Simon Yan
Sent: Wednesday, February 06, 2013 9:11 AM
To: Mara Kelly
Cc: tutor@python.org
Subject: Re: [Tutor] recursive function password check
On Wed, Feb 6, 2013 at 9:44 PM, Mara Kelly
mailto:schooluse1...@yahoo.com>> wrote:
Hi everyone, trying to write a program that has the user enter a password,
checks if it contains any vowels, and if it does prints ' It is false that
password(whatever the user enters) has no vowels,' and if it has no vowels
prints it is True that password has no vowels...
Here is what I have so far...
def password(y):
vowels=["a","e","i","o"]
if y[0] in vowels:
return False
if len(y) ==0:
return True
elif(y[len(y)-1] != vowels):
return False
else:
return password(y[1:len(y)-1])
x=input("Enter a password:")
print("It is", password(x),"that",x,"has no vowles")
As of now it just asks for the password, and then prints 'It is False that
password(whatever was entered) has no vowles' for any word I enter. I think
maybe some of my if statement conditions may be being returned to the function,
but then not printing the appropriate one? Can anyone help? Thanks!
It appears that the issue is from this:
elif(y[len(y)-1] != vowels):
This condition will be true because you are comparing a string with a list.
Thus causing passwrod() returning False.
___
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--
Regards,
YeeYaa (Simon Yan)
http://simonyan.fedorapeople.org/
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Re: [Tutor] recursive function password check
On 02/06/2013 09:26 AM, Noriko Tani wrote:
Hi Mara,
Several suggestions:
Put the password in a list, then loop each letter to check if it is a vowel
like this
No need to make it a list, strings are already iterable. And you don't
make it a list in the code, just in the remark above.
password=[]
vowels=['a','e','i','o','u']#in your message, u is missing, BTW
password=input("Enter a password:")
for p in password:
This loop goes around exactly once, since you return no matter what.
if p in vowels:
return True #I would use print("the message that you want to
display") though.
Shouldn't mix "calculation" and "output" unless it's just for play.
else:
return False
This return should be dedented to line up with the for statement, so it
only executes if none of the earlier characters was a vowel.
And how about error handling? You put
if len(y) ==0:
return True #I would use print("woops! You did not enter
anything.") and add break
But in the OP's code, this return is triggered on any string with no
vowels. Note, the function is recursive, and this is the only final
exit condition.
Does this password case sensitive? If so, add AEIOU in vowels list.
Good luck!
Noriko
From: Tutor [mailto:tutor-bounces+noriko.tani=tomtom@python.org] On Behalf
Of Simon Yan
Sent: Wednesday, February 06, 2013 9:11 AM
To: Mara Kelly
Cc: tutor@python.org
Subject: Re: [Tutor] recursive function password check
On Wed, Feb 6, 2013 at 9:44 PM, Mara Kelly
mailto:schooluse1...@yahoo.com>> wrote:
Hi everyone, trying to write a program that has the user enter a password,
checks if it contains any vowels, and if it does prints ' It is false that
password(whatever the user enters) has no vowels,' and if it has no vowels
prints it is True that password has no vowels...
Here is what I have so far...
def password(y):
vowels=["a","e","i","o"]
if y[0] in vowels:
return False
if len(y) ==0:
return True
elif(y[len(y)-1] != vowels):
return False
else:
return password(y[1:len(y)-1])
x=input("Enter a password:")
print("It is", password(x),"that",x,"has no vowles")
As of now it just asks for the password, and then prints 'It is False that
password(whatever was entered) has no vowles' for any word I enter. I think
maybe some of my if statement conditions may be being returned to the function,
but then not printing the appropriate one? Can anyone help? Thanks!
It appears that the issue is from this:
elif(y[len(y)-1] != vowels):
This condition will be true because you are comparing a string with a list.
Thus causing passwrod() returning False.
___
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--
Regards,
YeeYaa (Simon Yan)
http://simonyan.fedorapeople.org/
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--
DaveA
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Re: [Tutor] recursive function password check
On 02/06/2013 08:44 AM, Mara Kelly wrote:
Hi everyone, trying to write a program that has the user enter a password,
checks if it contains any vowels, and if it does prints ' It is false that
password(whatever the user enters) has no vowels,' and if it has no vowels
prints it is True that password has no vowels...
Here is what I have so far...def password(y):vowels=["a","e","i","o"]if y[0] in vowels:return False
if len(y) ==0:return Trueelif(y[len(y)-1] != vowels):return Falseelse:return password(y[1:len(y)-1])x=input("Enter a
password:")print("It is", password(x),"that",x,"has no vowles")
As of now it just asks for the password, and then prints 'It is False that
password(whatever was entered) has no vowles' for any word I enter. I think
maybe some of my if statement conditions may be being returned to the function,
but then not printing the appropriate one? Can anyone help? Thanks!
Please don't post in html email. It can seriously mess up your columns.
In your case, your email program didn't even try to provide a text
version, so those of us who read text emails can't make much sense of it.
Fortunately, I can decipher it by using someone else's reply. I quote
that below:
>
def password(y):
> vowels=["a","e","i","o"]
You might want to include "u" in that list. And maybe the uppercase
versions as well.
> if y[0] in vowels:
> return False
> if len(y) ==0:
> return True
> elif(y[len(y)-1] != vowels):
No, you want if y[-1] in vowels: instead. A string is never going to
be equal to a list.
> return False
> else:
> return password(y[1:len(y)-1])
> x=input("Enter a password:")
> print("It is", password(x),"that",x,"has no vowles")
I presume that making the function recursive was an explicit part of the
assignment.
--
DaveA
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Re: [Tutor] recursive function password check
Mara Kelly wrote:
> Hi everyone, trying to write a program that has the user enter a password,
> checks if it contains any vowels, and
> if it does prints ' It is false that password(whatever the user enters) has
> no vowels,' and if it has no vowels
> prints it is True that password has no vowels...
>
> Here is what I have so far...
> def password(y):
> vowels=["a","e","i","o"]
> if y[0] in vowels:
> return False
> if len(y) ==0:
> return True
> elif(y[len(y)-1] != vowels):
> return False
> else:
> return password(y[1:len(y)-1])
> x=input("Enter a password:")
> print("It is", password(x),"that",x,"has no vowles")
>
> As of now it just asks for the password, and then prints 'It is False that
> password(whatever was entered) has no
> vowles' for any word I enter. I think maybe some of my if statement
> conditions may be being returned to the
> function, but then not printing the appropriate one? Can anyone help? Thanks!
Why look at each character in the password? Unless you have a very short
password it will be more inefficient than looking for the vowels. Also,
if you lowercase the incoming password then you can avoid looking
for uppercase vowels. Note: if you have to deal with international
character sets (code pages) then you might not want to lower. If you
did not understand the previous statement, then chances are it does
not apply to you. :) I will leave the following code snippet with you
to adapt into your program.
y = y.lower()
if vowel in y:
return False
This email is confidential and subject to important disclaimers and
conditions including on offers for the purchase or sale of
securities, accuracy and completeness of information, viruses,
confidentiality, legal privilege, and legal entity disclaimers,
available at http://www.jpmorgan.com/pages/disclosures/email.
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Re: [Tutor] help with running perl script that writes to a text file
On 06/02/13 10:58, eryksun wrote: and pedantic comment about the habit of saying "DOS prompt". The cmd shell is a Win32 console application, unlike DOS command.com. Yes, but the problem is that Windows now has so many command prompts (cscript, cmd, power shell etc) that "the Windows prompt" would be meaningless and "the cmd prompt" too awkward to say, so "the DOS prompt" is both traditional and sufficiently specific making it the most easily understandable of the likely terms. -- Alan G 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] regarding the list problem
http://www.pythontutor.com/visualize.html is very helpful. Enter your code, click Visualize Execution, then click forward. -- 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] Tutor Digest, Vol 108, Issue 22
On Wed, Feb 6, 2013 at 3:00 AM, wrote:
> Send Tutor mailing list submissions to
> tutor@python.org
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://mail.python.org/mailman/listinfo/tutor
> or, via email, send a message with subject or body 'help' to
> tutor-requ...@python.org
>
> You can reach the person managing the list at
> tutor-ow...@python.org
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Tutor digest..."
>
>
> Today's Topics:
>
>1. Re: help with running perl script that writes to a text file
> (Peter Otten)
>2. Re: help with running perl script that writes to a text file
> (eryksun)
>
>
> --
>
> Message: 1
> Date: Wed, 06 Feb 2013 11:12:54 +0100
> From: Peter Otten <__pete...@web.de>
> To: tutor@python.org
> Subject: Re: [Tutor] help with running perl script that writes to a
> text file
> Message-ID:
> Content-Type: text/plain; charset="ISO-8859-1"
>
> 3n2 Solutions wrote:
>
>> Hello,
>>
>> I want to automate the following manual process from DOS promp:
>>
>> c:/scripts/perl>perl fix.pl base.gtx >base.txt
>>
>> Here is my python script:
>>
>> path="c:/scripts/perl/"
>> subprocess.call(['perl','fix.pl','base.gtx >base.txt',path])
>>
>> I also tried this alternative:
>>
>> subprocess.Popen(['perl','fix.pl','base.gtx >base.txt',path]) #same
>> result from this method.
>>
>> The above script generates the base.txt file but has no content in it.
>>
>> any ideas as to why the resulting text file is empty? Am I using the
>> correct python commands to run the above manual process?
>
> I'm surprised that base.txt is generated at all, I'd expect fix.pl to look
> for a file named "base.gtx >base.txt" and complain when it doesn't find
> that.
>
> I think the following should work:
>
> with open("c:/scripts/perl/base.txt", "w") as f:
> subprocess.check_call(
> ["perl",
> "c:/scripts/perl/fix.pl",
> "c:/scripts/perl/base.gtx"],
> stdout=f)
>
>
Peter, that did it! Thank you.
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[Tutor] If a method has no return type?
If a method has no return type? what will it return? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] If a method has no return type?
On Thu, Feb 7, 2013 at 12:09 AM, Sunil Tech wrote: > If a method has no return type? > what will it return? > note the original question is partially invalid... Python functions and methods aren't typed. however, i imagine the OP really meant *return value* instead, so the answer is really the following: functions *and* methods with no explicit return *value* return None... this happens when you either have no return statement or just return by itself with no object given. one exception is __init__()... you're never supposed to return anything from it... ever. i can't think of any others... can you? best regards, -- wesley - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - "A computer never does what you want... only what you tell it." +wesley chun : wescpy at gmail : @wescpy Python training & consulting : http://CyberwebConsulting.com "Core Python" books : http://CorePython.com Python blog: http://wescpy.blogspot.com ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] If a method has no return type?
Dear Sunil, No method or function in Python has a *static* return type. That's because Python is by nature a dynamic language, with duck typing and dynamic dispatch. In fact, any method or function may well return any of a number of different types: def crazy_function(return_int) if return_int: return 1 else: return 'foo' It's probably bad design, but there is nothing in the Python grammar and semantics that stops you from doing that. So your question is better phrased as: if I don't explicitly return anything, what is returned? The answer to that would be: the None object Cheers, Kal On 7 February 2013 14:09, Sunil Tech wrote: > If a method has no return type? > what will it return? > > ___ > Tutor maillist - Tutor@python.org > To unsubscribe or change subscription options: > http://mail.python.org/mailman/listinfo/tutor > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] help with running perl script that writes to a text file
On Wed, Feb 6, 2013 at 12:47 PM, Alan Gauld wrote: > so "the DOS prompt" is both traditional and sufficiently specific making it > the most easily understandable of the likely terms. "DOS prompt" is a common idiom, but it bears mentioning now and then that the OS is NT [1], not DOS. That's all; I know I'm being pedantic. Officially the Windows command-line shell is called the "command prompt". I call it the shell [2] or command line. Unless someone says PowerShell or 4NT, I assume it's cmd. [1] Windows 8 is NT 6.2.9200 [2] Not the GUI shell, Explorer, which is set here: HKLM\Software\Microsoft\Windows NT\CurrentVersion\WinLogon\Shell ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
