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Just starting to learn Python, and encounter a problem

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  Just starting to learn Python, and encounter a problem Zagyen Leo <zagyen@gmail.com> - 2016-07-22 06:59 -0700
    Re: Just starting to learn Python, and encounter a problem Random832 <random832@fastmail.com> - 2016-07-22 10:30 -0400
      Re: Just starting to learn Python, and encounter a problem Zagyen Leo <zagyen@gmail.com> - 2016-07-22 23:13 -0700
    Re: Just starting to learn Python, and encounter a problem Bob Gailer <bgailer@gmail.com> - 2016-07-22 10:36 -0400
      Re: Just starting to learn Python, and encounter a problem gst <g.starck@gmail.com> - 2016-07-23 11:18 -0700
        Re: Just starting to learn Python, and encounter a problem MRAB <python@mrabarnett.plus.com> - 2016-07-23 20:06 +0100
        Re: Just starting to learn Python, and encounter a problem Steven D'Aprano <steve@pearwood.info> - 2016-07-24 11:58 +1000
    Re: Just starting to learn Python, and encounter a problem Gordon Levi <gordon@address.invalid> - 2016-07-23 00:37 +1000
      Re: Just starting to learn Python, and encounter a problem justin walters <walters.justin01@gmail.com> - 2016-07-22 08:04 -0700
    Re: Just starting to learn Python, and encounter a problem MRAB <python@mrabarnett.plus.com> - 2016-07-22 16:08 +0100

#111750 — Just starting to learn Python, and encounter a problem

yeah, it may be quite simple to you experts, but hard to me.

In one of exercises from the Tutorial it said: "Write a program that asks the user their name, if they enter your name say "That is a nice name", if they enter "John Cleese" or "Michael Palin", tell them how you feel about them ;), otherwise tell them "You have a nice name."

And i write so:

name = input("Enter your name here: ")
if name == "John Cleese" or "Michael Palin":
    print("Sounds like a gentleman.")
else:
    print("You have a nice name.")

But strangely whatever I type in (e.g. Santa Claus), it always say "Sounds like a gentleman.", not the result I want.

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#111752

On Fri, Jul 22, 2016, at 09:59, Zagyen Leo wrote:
> yeah, it may be quite simple to you experts, but hard to me.
> 
> In one of exercises from the Tutorial it said: "Write a program that asks
> the user their name, if they enter your name say "That is a nice name",
> if they enter "John Cleese" or "Michael Palin", tell them how you feel
> about them ;), otherwise tell them "You have a nice name."
> 
> And i write so:
> 
> name = input("Enter your name here: ")
> if name == "John Cleese" or "Michael Palin":
>     print("Sounds like a gentleman.")
> else:
>     print("You have a nice name.")
> 
> But strangely whatever I type in (e.g. Santa Claus), it always say
> "Sounds like a gentleman.", not the result I want.

"or" is a lower precedence than "==".

> if name == "John Cleese" or "Michael Palin"

becomes if (name == "John Cleese") or "Michael Palin"; becomes if False
or "Michael Palin"; becomes if "Michael Palin"; and non-empty strings
are considered true.

You want if Name == "John Cleese" or Name == "Michael Palin"; or if Name
in ("John Cleese", "Michael Palin")

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#111780

I got it! Thank you.

Hope in one day I could help other newbies as you do.

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#111753

On Jul 22, 2016 10:00 AM, "Zagyen Leo" <zagyen@gmail.com> wrote:
>
> yeah, it may be quite simple to you experts, but hard to me.
>
> In one of exercises from the Tutorial it said: "Write a program that asks
the user their name, if they enter your name say "That is a nice name", if
they enter "John Cleese" or "Michael Palin", tell them how you feel about
them ;), otherwise tell them "You have a nice name."
>
> And i write so:
>
> name = input("Enter your name here: ")
> if name == "John Cleese" or "Michael Palin":
>     print("Sounds like a gentleman.")
> else:
>     print("You have a nice name.")
>
> But strangely whatever I type in (e.g. Santa Claus), it always say
"Sounds like a gentleman.", not the result I want.

Even without knowing the operator precedence, this will be evaluated either
as:
(name == "John Cleese") or "Michael Palin")
or:
name == ("John Cleese" or "Michael Palin").

Case 1: (name == "John Cleese")  evaluates to either True or False. False
or "Michael Palin" evaluates to  ( believe it or not) " Michael Palin"!
Which, as far as if is concerned, is True. True or "Michael Palin"
evaluates to True.

Case 2: "John Cleese" or "Michael Palin" evaluates to False; name== False
evaluates to False.

One way to get the results you want:
if name in ("John Cleese" or "Michael Palin"):

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#111796

Heuh case 2 :

"String1" or "String2" 

Evaluates to "String1" ?

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#111797

On 2016-07-23 19:18, gst wrote:
> Heuh case 2 :
>
> "String1" or "String2"
>
> Evaluates to "String1" ?
>
Suppose you have:

     x or y

If bool(x) returns True, then the result will be x, else the result will 
be y.

Example 1:

bool("String1") returns True, therefore the result of:

     "String1" or "String2"

is "String1".

Example 2:

bool("") returns False, so the result of:

     "" or "String2"

is "String2".

(The empty string "" is considered 'false-y'; all other strings (i.e. 
all non-empty strings) are considered 'true-y'.)

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#111798

On Sun, 24 Jul 2016 04:18 am, gst wrote:

> Heuh case 2 :
> 
> "String1" or "String2"
> 
> Evaluates to "String1" ?


Correct. What did you expect?

Have you read the Fine Manual?


https://docs.python.org/3/reference/expressions.html#boolean-operations



-- 
Steven
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.

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#111754

Zagyen Leo <zagyen@gmail.com> wrote:

>yeah, it may be quite simple to you experts, but hard to me.
>
>In one of exercises from the Tutorial it said: "Write a program that asks the user their name, if they enter your name say "That is a nice name", if they enter "John Cleese" or "Michael Palin", tell them how you feel about them ;), otherwise tell them "You have a nice name."
>
>And i write so:
>
>name = input("Enter your name here: ")
>if name == "John Cleese" or "Michael Palin":
>    print("Sounds like a gentleman.")
>else:
>    print("You have a nice name.")
>
>But strangely whatever I type in (e.g. Santa Claus), it always say "Sounds like a gentleman.", not the result I want.

The second line should be 
if name == "John Cleese" or name == "Michael Palin":

As discussed in recent lengthy thread in this group the following
line, and hence your statement, is always true -

If "Michael Palin":

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#111757

:
On Jul 22, 2016 7:46 AM, "Gordon Levi" <gordon@address.invalid> wrote:
>
> Zagyen Leo <zagyen@gmail.com> wrote:
>
> >yeah, it may be quite simple to you experts, but hard to me.
> >
> >In one of exercises from the Tutorial it said: "Write a program that
asks the user their name, if they enter your name say "That is a nice
name", if they enter "John Cleese" or "Michael Palin", tell them how you
feel about them ;), otherwise tell them "You have a nice name."
> >
> >And i write so:
> >
> >name = input("Enter your name here: ")
> >if name == "John Cleese" or "Michael Palin":
> >    print("Sounds like a gentleman.")
> >else:
> >    print("You have a nice name.")
> >
> >But strangely whatever I type in (e.g. Santa Claus), it always say
"Sounds like a gentleman.", not the result I want.
>
> The second line should be
> if name == "John Cleese" or name == "Michael Palin":
>
> As discussed in recent lengthy thread in this group the following
> line, and hence your statement, is always true -
>
> If "Michael Palin":
> --
> https://mail.python.org/mailman/listinfo/python-list

The easiest way to right this would be to use a tuple like so:

    if name in ('John Cleese', 'Michael Palin'):
        print ('They sound like a gentleman')

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#111758

On 2016-07-22 14:59, Zagyen Leo wrote:
> yeah, it may be quite simple to you experts, but hard to me.
>
> In one of exercises from the Tutorial it said: "Write a program that asks the user their name, if they enter your name say "That is a nice name", if they enter "John Cleese" or "Michael Palin", tell them how you feel about them ;), otherwise tell them "You have a nice name."
>
> And i write so:
>
> name = input("Enter your name here: ")
> if name == "John Cleese" or "Michael Palin":
>     print("Sounds like a gentleman.")
> else:
>     print("You have a nice name.")
>
> But strangely whatever I type in (e.g. Santa Claus), it always say "Sounds like a gentleman.", not the result I want.
>
This bit:

     name == "John Cleese" or "Michael Palin"

means the same as:

     (name == "John Cleese") or "Michael Palin"

If name is "Santa Claus", that's:

     "Santa Claus" == "John Cleese" or "Michael Palin"

which is:

     False or "Michael Palin"

which is:

     "Michael Palin"

and any string except "" is treated as True.

The condition should be:

     name == "John Cleese" or name == "Michael Palin"

(Shorter alternatives are available; you'll learn about them later!)

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