[Tutor] Tutor Digest, Vol 147, Issue 52
marat murad
min786a at googlemail.com
Wed Jun 1 07:43:25 EDT 2016
Thanks for your replies,I think I understand it much better now. I Also I
wanted to know what the 'None' does in the second program.
Thanks in Advance
Minhaj
On Wed, Jun 1, 2016 at 1:59 AM, <tutor-request at python.org> wrote:
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> Today's Topics:
>
> 1. Help with 'if' statement and the concept of None (marat murad)
> 2. Python OLS help (Vadim Katsemba)
> 3. Re: Help with 'if' statement and the concept of None (Alan Gauld)
> 4. Re: Python OLS help (Alan Gauld)
> 5. Re: Help with 'if' statement and the concept of None
> (Steven D'Aprano)
> 6. Re: Help with 'if' statement and the concept of None (Ben Finney)
>
>
> ---------- Forwarded message ----------
> From: marat murad <min786a at googlemail.com>
> To: tutor at python.org
> Cc:
> Date: Tue, 31 May 2016 16:16:21 +0100
> Subject: [Tutor] Help with 'if' statement and the concept of None
> Hi
> I'm learning how to code with python an I have purchased the book 'Python
> Programming for the absolute beginner,third edition' by Michael Dawson.
> There is one concept that is confusing me in chapter 3 page 71 there is a
> program whose code I have pasted below. The author introduced a new way of
> coding the Boolean NOT operator with the 'if' statement I have highlighted
> the relevant area,apparently this if statement actually means if money !=
> 0,which I understood,but the program below this one which introduces the
> idea of slicing also has a if statement similar to the first one,except the
> second one accepts 0 value but the first one doesn't.
>
> print("Welcome to the Chateau D'food")
> print("It seems we are quit full today.\n")
>
> money = int(input("How many dollars do you slip the Maitr D'? "))
>
> *if money:*
> print("Ah I think I can make something work")
> else:
> print("Please sit ,it may be a while")
>
>
> input("\nPress enter to exit")
>
>
> The slicing program
>
> word = "existential"
>
> print("Enter the beginning and ending index for the word existential")
> print("press he enter key at 'Start' to exit")
>
> start= None
> while start != "":
> start=input("\nStart: ")
>
> * if start:*
> start=int(start)
>
> finish=int(input("Finish: "))
>
> print ("word[",start, ":",finish, "]is " , end="")
> print(word[start:finish])
>
> input("\nPress enter to exit")
>
> I hope i made sense.
>
> Thankyou
>
>
>
> ---------- Forwarded message ----------
> From: Vadim Katsemba <vkatz722 at gmail.com>
> To: tutor at python.org
> Cc:
> Date: Tue, 31 May 2016 11:30:29 -0400
> Subject: [Tutor] Python OLS help
> Hello there, I am having trouble running the Ordinary Least Squares (OLS)
> regression on Spyder. I typed in lm =
> smf.ols(formula='LATITUDE~DIAMETER',data=dataf).fit(), and I ended up
> getting this error: ValueError: For numerical factors, num_columns must be
> an int. How am I supposed to run the OLS, is there another module I need to
> use? Any help would be appreciated.
>
>
>
> ---------- Forwarded message ----------
> From: Alan Gauld <alan.gauld at yahoo.co.uk>
> To: tutor at python.org
> Cc:
> Date: Tue, 31 May 2016 23:06:47 +0100
> Subject: Re: [Tutor] Help with 'if' statement and the concept of None
> On 31/05/16 16:16, marat murad via Tutor wrote:
>
> > program whose code I have pasted below. The author introduced a new way
> of
> > coding the Boolean NOT operator with the 'if' statement I have
> highlighted
> > the relevant area,apparently this if statement actually means if money !=
> > 0,which I understood,
>
> Boolean values are either true or false.
> Other values are given boolean equivalent values by Python.
> eg. For strings an empty string is False, anything else is True.
> For numbers 0 is False anything else is True.
>
> So in your example:
>
> > *if money:*
> > print("Ah I think I can make something work")
> > else:
> > print("Please sit ,it may be a while")
> >
>
> The first 'if' test is saying
>
> 'if money is equivalent to True' (anything other than zero)
>
> In effect that's the same as you said (it's like testing for != 0)
> but the important difference is that it is relying
> on the boolean *equivalence* of an integer value.
> The same is true in your second example:
>
> > idea of slicing also has a if statement similar to the first one,except
> the
> > second one accepts 0 value but the first one doesn't.
> >
>
> > start=input("\nStart: ")
> >
> > * if start:*
> > start=int(start)
>
> Again this is really saying if start is True and for a string
> (which is what input() returns), as I said above, True means
> not empty. So the string '0' is not empty and therefore True.
> It's not the value of the character that matters it's the fact
> that there is a character there at all.
>
> All objects in Python have these boolean equivalent values,
> for example an empty list, tuple,set or dictionary is also
> considered False. As is the special value None.
>
> > I hope i made sense.
>
> Yes, although your subject also mentions the concept of None?
> Did you have another question about that?
>
> HTH
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
>
>
>
> ---------- Forwarded message ----------
> From: Alan Gauld <alan.gauld at yahoo.co.uk>
> To: tutor at python.org
> Cc:
> Date: Tue, 31 May 2016 23:10:49 +0100
> Subject: Re: [Tutor] Python OLS help
> On 31/05/16 16:30, Vadim Katsemba wrote:
> > Hello there, I am having trouble running the Ordinary Least Squares (OLS)
> > regression on Spyder.
>
> I had no idea what Spyder was but a Google search says its an IDE
> somewhat akin to matlab or IPython... It also has a discussion group:
>
> http://groups.google.com/group/spyderlib
>
> You may find someone on this list who knows it but you will likely
> get a better response on the spyder forum. This list is really
> for core python language questions and although we try to be
> helpful on other matters a dedicated forum is usually better.
>
>
> --
> Alan G
> Author of the Learn to Program web site
> http://www.alan-g.me.uk/
> http://www.amazon.com/author/alan_gauld
> Follow my photo-blog on Flickr at:
> http://www.flickr.com/photos/alangauldphotos
>
>
>
>
>
> ---------- Forwarded message ----------
> From: "Steven D'Aprano" <steve at pearwood.info>
> To: tutor at python.org
> Cc:
> Date: Wed, 1 Jun 2016 10:12:08 +1000
> Subject: Re: [Tutor] Help with 'if' statement and the concept of None
> On Tue, May 31, 2016 at 04:16:21PM +0100, marat murad via Tutor wrote:
>
> > money = int(input("How many dollars do you slip the Maitr D'? "))
> > *if money:*
> > print("Ah I think I can make something work")
> > else:
> > print("Please sit ,it may be a while")
>
> All values in Python can be used where a true or false boolean value is
> expected, such as in an "if" or a "while" statement. We call this a
> "boolean context", meaning something which expects a true or false flag.
>
> So we have True and False (with the initial capital letter) as special
> constants, but we also can treat every other value as if they were true
> or false (without the initial capital). Sometimes we call them "truthy"
> and "falsey", or "true-like" and "false-like" values.
>
> For Python built-ins, we have:
>
> Falsey (false-like) values:
>
> - zero: 0, 0.0, 0j, Fraction(0), etc.
> - empty strings: "", b""
> - empty containers: [], (), {}, set() etc.
> (empty list, empty tuple, empty dict, empty set)
> - sequences with len() == 0
> - None
> - False
>
> Truthy (true-like) values:
>
> - non-zero numbers: 1, 2.0, 3j, Fraction(4, 5), etc.
> - non-empty strings: "Hello world!", b"\x0"
> (yes, even the null-byte is non-empty, since it has length 1)
> - non-empty containers
> - sequences with len() != 0
> - classes, object()
> - True
>
> We say that "false values represent nothing", like zero, empty strings,
> None, and empty containers; while "true values represent something",
> that is, anything which is not nothing.
>
>
> So any time you have a value, say, x, we can test to see if x is a
> truthy or falsey value:
>
>
> values = [1, 5, 0, -2.0, 3.7, None, object(), (1, 2), [], True]
> for x in values:
> if x:
> print(x, "is a truthy value")
> else:
> print(x, "is a falsey value")
>
>
>
>
> --
> Steve
>
>
>
> ---------- Forwarded message ----------
> From: Ben Finney <ben+python at benfinney.id.au>
> To: tutor at python.org
> Cc:
> Date: Wed, 01 Jun 2016 10:58:58 +1000
> Subject: Re: [Tutor] Help with 'if' statement and the concept of None
> marat murad via Tutor <tutor at python.org> writes:
>
> > The author introduced a new way of coding the Boolean NOT operator
> > with the 'if' statement I have highlighted the relevant
> > area,apparently this if statement actually means if money != 0,which I
> > understood
>
> Not quite. The statement actually means “if ‘money’ evaluates as true”.
>
> Any Python value can be interrogated with the question “Are you true or
> false?”, and that is what the ‘if’ statement does.
>
> This is different from asking ”Is this the True constant or the False
> constant?” because for most values the answer is ”Neither”.
>
> In Python the question “Is this value true, or false?” is usually
> implemented as ”Is this value something, or nothing?”. If the value is
> conceptually nothing, it evaluates as false when interrogated in a
> boolean context.
>
> See the Python documentation for a comprehensive list of false values
> <URL:https://docs.python.org/3/library/stdtypes.html#truth-value-testing>;
> any not-false value is true by default.
>
> If you learn the conceptual “if it's not something, it's false”, then
> you will have a fairly good intuition for how ‘if somevalue’ works.
>
> --
> \ “None can love freedom heartily, but good men; the rest love |
> `\ not freedom, but license.” —John Milton |
> _o__) |
> Ben Finney
>
>
>
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