Re: [Tutor] floats
"Michael bridges" wrote i want to 10 / 1000 and get 0.01 not 0 if 1000 is made 1000.00 then 0.01 is printed but that gives 500 / 1000.00 is 0.5 not 0.50 can someone till me how to get a two decimal precision every time? You are confusing two different things.. The first case is that of integer versus float division. You solve that by either explicitly making one of the numbers a float or by converting to float using the foloat() operation. The second issue is the *representation* of the result. The number of decimal places displayed is a matter of representation only, the actual value stored will not change. Thus 0.5 and 0.50 and 0.5000 are all the same value in memory, it is only how they are printed that changes and that is controlled by how you choose to format the display. Typically you use a format string: res = 10/float(20) "%f" % res "%7.3f" % res "%5.1f" % res "%6e" % res "%6.4g" % res 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] floats
ok, will attempt to clarify. i want to out put of two numbers [int or float or anything] to be x.xx not x.x. i want two numbers after the decimal not one. --- On Tue, 6/7/11, Alan Gauld wrote: > From: Alan Gauld > Subject: Re: [Tutor] floats > To: tutor@python.org > Date: Tuesday, June 7, 2011, 1:16 AM > > "Michael bridges" > wrote > > > i want to 10 / 1000 and get 0.01 not 0 > > if 1000 is made 1000.00 then 0.01 is printed > > but that gives 500 / 1000.00 is 0.5 not 0.50 > > > > can someone till me how to get a two decimal precision > every time? > > You are confusing two different things.. > The first case is that of integer versus float division. > You solve that by either explicitly making one of the > numbers a float or by converting to float using the > foloat() operation. > > The second issue is the *representation* of the result. > The number of decimal places displayed is a matter > of representation only, the actual value stored will not > change. Thus 0.5 and 0.50 and 0.5000 are all > the same value in memory, it is only how they are > printed that changes and that is controlled by how > you choose to format the display. > > Typically you use a format string: > > res = 10/float(20) > "%f" % res > "%7.3f" % res > "%5.1f" % res > "%6e" % res > "%6.4g" % res > > > 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 > ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] floats
Hello Michael On 7 June 2011 21:10, Michael bridges wrote: > ok, will attempt to clarify. > i want to out put of two numbers [int or float or anything] to be x.xx not > x.x. > i want two numbers after the decimal not one. > > Alan's already given you exactly the correct answer. Have you tried his suggestions? What did you not understand or what problems did you run into? Here's a little example from an interactive Python interpreter session which shows you how you can play with these concepts to help clarify your understanding: Python 2.7 (r27:82525, Jul 4 2010, 07:43:08) [MSC v.1500 64 bit (AMD64)] on win 32 Type "help", "copyright", "credits" or "license" for more information. >>> res = 10/float(20) >>> res 0.5 >>> "%f" % res '0.50' >>> "%7.3f" % res ' 0.500' >>> str = "%6e" % res >>> str '5.00e-01' >>> print str 5.00e-01 >>> Regards, Walter ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
[Tutor] if statement
i'm very new to python (currently going through a python for beginners
book at work to pass the time), and i'm having trouble with an if
statement exercise. basically, i'm creating a very simple password
program that displays "Access Granted" if the if statement is true.
the problem i'm having is that no matter what i set the password to,
it seems like it's ignoring the if statement (and failing to print
"Access Granted"). the code is copied below. i'm pretty sure it's my
own programming ignorance, but i would greatly appreciate any
feedback.
# Granted or Denied
# Demonstrates an else clause
print("Welcome to System Security Inc.")
print("-- where security is our middle name\n")
password = input("Enter your password: ")
if password == "a":
print("Access Granted")
input("\n\nPress the enter key to exit.")
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Re: [Tutor] if statement
On Tue, Jun 7, 2011 at 11:26 PM, Matthew Brunt wrote:
> i'm very new to python (currently going through a python for beginners
> book at work to pass the time), and i'm having trouble with an if
> statement exercise. basically, i'm creating a very simple password
> program that displays "Access Granted" if the if statement is true.
> the problem i'm having is that no matter what i set the password to,
> it seems like it's ignoring the if statement (and failing to print
> "Access Granted"). the code is copied below. i'm pretty sure it's my
> own programming ignorance, but i would greatly appreciate any
> feedback.
Actually, no, this case it's not your ignorance. What is probably
going on is that you are using Python 2, but the book is going with
Python 3. I won't get into the details, but the function that does
what input() does in Python 3, is called raw_input() in Python 2 (and
the Python 2 input() function is advised against using for security
reasons). Probably if you change input to raw_input in your program,
it does do what you want it to do.
> # Granted or Denied
> # Demonstrates an else clause
>
> print("Welcome to System Security Inc.")
> print("-- where security is our middle name\n")
>
> password = input("Enter your password: ")
>
> if password == "a":
> print("Access Granted")
>
> input("\n\nPress the enter key to exit.")
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>
--
André Engels, andreeng...@gmail.com
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[Tutor] Copying a mutable
Hi, let X be a mutable container, such as dict/set/list=bytearray, and Y=X, When I change X, Y will follow it, having always the same value, although id(X)!=id(Y). How is that, what is the explanation? Meanwhile the same for immutable types results a real copy, and so does for simple mutables such as int. I suspect it has something to do with pointers, but what is the difference between mutables and immutables, and why have they different id's if they are the same? ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] if statement
"Andre Engels" wrote Actually, no, this case it's not your ignorance. What is probably going on is that you are using Python 2, but the book is going with Python 3. You can quickly check the version by just typing python at an OS command prompt to get into the interactive interpreter(>>>). The welcome message should tell you the version you are running. 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] Copying a mutable
Apologies for the top post, my phone doesn't allow editing the message body. You are slightly confused - ints are not mutable! You can combine or multiply them, along with several other operations, but they are certainly not mutable. The easiest way to check is use them as keys in a dict. You can't do that with lists or other mutable types. Since I don't have computer access right now I can't look up the docs on id, but hopefully someone else can enlighten you. But ints are definitely immutable. I suspect you're confusing the fact that you can easily reassign ints with mutability. HTH, Wayne On Jun 7, 2011 5:50 PM, "Válas Péter" wrote: Hi, let X be a mutable container, such as dict/set/list=bytearray, and Y=X, When I change X, Y will follow it, having always the same value, although id(X)!=id(Y). How is that, what is the explanation? Meanwhile the same for immutable types results a real copy, and so does for simple mutables such as int. I suspect it has something to do with pointers, but what is the difference between mutables and immutables, and why have they different id's if they are the same? ___ 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] Copying a mutable
2011. június 8. 1:02 Wayne Werner írta, : > You are slightly confused - ints are not mutable! > All right, I was really wrong in this question (here it is after midnight :-), but this doesn't make an influence on the main question. ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Copying a mutable
Hi, 2011/6/7 Válas Péter > Hi, > > let X be a mutable container, such as dict/set/list=bytearray, and Y=X, > When I change X, Y will follow it, having always the same value, although > id(X)!=id(Y). That's not correct: Python 2.7 (r27:82525, Jul 4 2010, 07:43:08) [MSC v.1500 64 bit (AMD64)] on win 32 Type "help", "copyright", "credits" or "license" for more information. >>> x=[1,2,3] >>> y=x >>> id(x) 36115464L >>> id(y) 36115464L >>> x.append(4) >>> id(x) 36115464L >>> id(y) 36115464L >>> x [1, 2, 3, 4] >>> As you can see, x and y are references to the same object (e.g. with the same id.) Regards Walter ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Copying a mutable
unsubscribe 在 2011-06-08 07:11:33，"Walter Prins" 写道： Hi, 2011/6/7 Válas Péter Hi, let X be a mutable container, such as dict/set/list=bytearray, and Y=X, When I change X, Y will follow it, having always the same value, although id(X)!=id(Y). That's not correct: Python 2.7 (r27:82525, Jul 4 2010, 07:43:08) [MSC v.1500 64 bit (AMD64)] on win 32 Type "help", "copyright", "credits" or "license" for more information. >>> x=[1,2,3] >>> y=x >>> id(x) 36115464L >>> id(y) 36115464L >>> x.append(4) >>> id(x) 36115464L >>> id(y) 36115464L >>> x [1, 2, 3, 4] >>> As you can see, x and y are references to the same object (e.g. with the same id.) Regards Walter ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Copying a mutable
On 01/-10/-28163 02:59 PM, Válas Péter wrote: Hi, let X be a mutable container, such as dict/set/list=bytearray, and Y=X, When I change X, Y will follow it, having always the same value, although id(X)!=id(Y). How is that, what is the explanation? Meanwhile the same for immutable types results a real copy, and so does for simple mutables such as int. I suspect it has something to do with pointers, but what is the difference between mutables and immutables, and why have they different id's if they are the same? It would help greatly if you actually posted some code that showed your confusion, since there are several errors in your message. As Wayne pointed out, integers are immutable. There are no methods on them that modify them in place. All you can do is bind a variable to a different integer object. Further, if you set Y=X, the id's will be the same. Try it, and paste the actual test into your message. Don't just paraphrase. Python 2.7.1+ (r271:86832, Apr 11 2011, 18:13:53) [GCC 4.5.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> x = [4, 5,6] >>> y = x >>> id(y) 24789144 >>> id(x) 24789144 Now, if you change x by doing an append, for example, they both change: You mutated the object to which they both refer. >>> x.append(42) >>> x [4, 5, 6, 42] >>> y [4, 5, 6, 42] >>> But if you rebind one of them, then they can diverge: >>> x = [3] >>> x [3] >>> y [4, 5, 6, 42] >>> id(x) 24978568 >>> id(y) 24789144 Now you can notice that x has a different id. It's bound to a different object. Now, if an object is immutable, then the question of what happens when you change the object is nonsensical. Since you can't change it, you don't really care if the two names are bound to same object, or just to two objects that happen to have the same value. One more thing. Binding happens in an assignment, but it also happens in a function call, and in some import syntaxes and in for loops, generator expressions, and list comprehensions. Some of that behavior can change between different versions of Python, so if you start getting into those corners, you'll have to be more specific. HTH DaveA ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
Re: [Tutor] Copying a mutable
Walter and Dave, thank you for the useful and detailed answer, now I see it better. I didn't write code, because once I realized I had spoiled something, the mistake has no more importance except historical, the correct solutions have importance. 2011. június 8. 4:19 Dave Angel írta, : > Now, if an object is immutable, then the question of what happens when you > change the object is nonsensical. Since you can't change it, you don't > really care if the two names are bound to same object, or just to two > objects that happen to have the same value. > Being one of the purposes of Python to be a simple educational language, I want to make this simple to a beginner who does care. :-) Here is a piece of code, Python 3.1.2, a small game with a list and a tuple: >>> li=[3,4] >>> id(li) 13711200 >>> la=li >>> id(la) 13711200 >>> li*=4 >>> li [3, 4, 3, 4, 3, 4, 3, 4] >>> la [3, 4, 3, 4, 3, 4, 3, 4] >>> id(li) 13711200 >>> tup=(3,4) >>> id(tup) 13697392 >>> top=tup >>> id(top) 13697392 >>> tup*=4 >>> tup (3, 4, 3, 4, 3, 4, 3, 4) >>> top (3, 4) >>> id(tup) 12956016 >>> id(top) 13697392 My question is: how would you explain the different behaviour of a list and a tuple for a beginner? Formally we made the same intervention to these poor guys, the list and the tuple, they look the same except parenthesis and square bracket, but they reacted differently. Although tuples are immutable, the beginner only sees that they have changed in the same way. This is another point the beginner may be confused: multiple assignments. Formally we play the same game with an int and a list, and they will again react in a different way. >>> n=m=8 >>> m*=8 >>> m 64 >>> n 8 >>> n=m=[2,3] >>> m*=8 >>> m [2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3] >>> n [2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3, 2, 3] > > One more thing. Binding happens in an assignment, but it also happens in a > function call, and in some import syntaxes and in for loops, generator > expressions, and list comprehensions. Just to precisely understand English words, because this is a foreign language for me. As far as I understand, assignment means giving a value to a variable which is the expression used by classical languages that have variables (such as Pascal or Basic). Python has no variables, since even the simpliest data is an object, but we still say assignment, because it is comfortable. In this sense, if I say, "assignment" is a subset of "binding", is it correct? Péter ___ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
