Velocity Reviews > Basic question

# Basic question

Dmitry Dzhus
Guest
Posts: n/a

 05-12-2007

> Actually I'm trying to convert a string to a list of float numbers:
> str = '53,20,4,2' to L = [53.0, 20.0, 4.0, 2.0]

str="53,20,4,2"
map(lambda s: float(s), str.split(','))

Last expression returns: [53.0, 20.0, 4.0, 2.0]
--
Happy Hacking.

Dmitry "Sphinx" Dzhus
http://sphinx.net.ru

Grant Edwards
Guest
Posts: n/a

 05-12-2007
On 2007-05-12, Cesar G. Miguel <(E-Mail Removed)> wrote:

> Actually I'm trying to convert a string to a list of float numbers:
> str = '53,20,4,2' to L = [53.0, 20.0, 4.0, 2.0]

>>> str = '53,20,4,2'

>>> [float(w) for w in str.split(',')]

[53.0, 20.0, 4.0, 2.0]

>>> map(float,str.split(','))

[53.0, 20.0, 4.0, 2.0]

--
Grant Edwards grante Yow! I want you to
at MEMORIZE the collected
visi.com poems of EDNA ST VINCENT
MILLAY... BACKWARDS!!

Grant Edwards
Guest
Posts: n/a

 05-12-2007
On 2007-05-12, Dmitry Dzhus <(E-Mail Removed)> wrote:

> str="53,20,4,2"
> map(lambda s: float(s), str.split(','))

There's no need for the lambda.

map(float,str.split(','))

Does exactly the same thing.

--
Grant Edwards grante Yow! I feel like I am
at sharing a "CORN-DOG" with
visi.com NIKITA KHRUSCHEV...

Cesar G. Miguel
Guest
Posts: n/a

 05-12-2007
On May 12, 3:40 pm, Dmitry Dzhus <(E-Mail Removed)> wrote:
> > Actually I'm trying to convert a string to a list of float numbers:
> > str = '53,20,4,2' to L = [53.0, 20.0, 4.0, 2.0]

>
> str="53,20,4,2"
> map(lambda s: float(s), str.split(','))
>
> Last expression returns: [53.0, 20.0, 4.0, 2.0]
> --
> Happy Hacking.
>
> Dmitry "Sphinx" Dzhushttp://sphinx.net.ru

Nice!

The following also works using split and list comprehension (as
suggested in a brazilian python forum):

-------------------
L = []
file = ['5,1378,1,9', '2,1,4,5']
str=''
for item in file:
L.append([float(n) for n in item.split(',')])
-------------------

Thank you for all suggestions!

Kirk Job Sluder
Guest
Posts: n/a

 05-12-2007
"Cesar G. Miguel" <(E-Mail Removed)> writes:

> I've been studying python for 2 weeks now and got stucked in the
> following problem:
>
> for j in range(10):
> print j
> if(True):
> j=j+2
> print 'interno',j
>
> What happens is that "j=j+2" inside IF does not change the loop
> counter ("j") as it would in C or Java, for example.

Granted this question has already been answered in parts, but I just
wanted to elaborate.

Although the python for/in loop is superficially similar to C and Java
for loops, they work in very different ways. Range creates a list
object that can create an iterator, and the for/in construct under the
hood sets j to the results of iterator.next(). The equivalent
completely untested java would be something like:

public ArrayList<Object> range(int n){
a = new ArrayList<Object>; //Java 1.5 addition I think.
for(int x=0,x<n,x++){
}
return a;
}

Iterator i = range(10).iterator();

Integer j;
while i.hasNext(){
j = i.next();
system.out.println(j.toString());
j = j + 2;
system.out.println("interno" + j.toString());
}

This probably has a bunch of bugs. I'm learning just enough java
these days to go with my jython.

1: Python range() returns a list object that can be expanded or
modified to contain arbitrary objects. In java 1.5 this would be one
of the List Collection objects with a checked type of
java.lang.Object. So the following is legal for a python list, but
would not be legal for a simple C++ or Java array.

newlist = range(10)
newlist[5] = "foo"
newlist[8] = open("filename",'r')

2: The for/in loop takes advantage of the object-oriented nature of
list objects to create an iterator for the list, and then calls
iterator.next() until the iterator runs out of objects. You can do
this in python as well:

i = iter(range(10))
while True:
try:
j = i.next()
print j
j = j + 2
print j
except StopIteration:
break

Python lists are not primitive arrays, so there is no need to
explicitly step through the array index by index. You can also use an
iterator on potentially infinite lists, streams, and generators.

Another advantage to for/in construction is that loop counters are
kept nicely separate from the temporary variable, making it more
difficult to accidentally short-circuit the loop. If you want a loop
with the potential for a short-circuit, you should probably use a
while loop:

j = 0
while j < 10:
if j == 5:
j = j + 2
else:
j = j + 1
print j

>
> Am I missing something?
>
> []'s
> Cesar
>

--
Kirk Job Sluder

Alex Martelli
Guest
Posts: n/a

 05-12-2007
Cesar G. Miguel <(E-Mail Removed)> wrote:

> On May 12, 3:40 pm, Dmitry Dzhus <(E-Mail Removed)> wrote:
> > > Actually I'm trying to convert a string to a list of float numbers:
> > > str = '53,20,4,2' to L = [53.0, 20.0, 4.0, 2.0]

> >
> > str="53,20,4,2"
> > map(lambda s: float(s), str.split(','))
> >
> > Last expression returns: [53.0, 20.0, 4.0, 2.0]
> > --
> > Happy Hacking.
> >
> > Dmitry "Sphinx" Dzhushttp://sphinx.net.ru

>
> Nice!

As somebody else alredy pointed out, the lambda is supererogatory (to
say the least).

> The following also works using split and list comprehension (as
> suggested in a brazilian python forum):
>
> -------------------
> L = []
> file = ['5,1378,1,9', '2,1,4,5']
> str=''
> for item in file:
> L.append([float(n) for n in item.split(',')])

The assignment to str is useless (in fact potentially damaging because
you're hiding a built-in name).

L = [float(n) for item in file for n in item.split(',')]

is what I'd call Pythonic, personally (yes, the two for clauses need to
be in this order, that of their nesting).

Alex

sturlamolden
Guest
Posts: n/a

 05-12-2007
On May 12, 6:18 pm, "Cesar G. Miguel" <(E-Mail Removed)> wrote:

> Am I missing something?

Python for loops iterates over the elements in a container. It is
similar to Java's "for each" loop.

for j in range(10):
print j
if(True):
j=j+2
print 'interno',j

Is equivalent to:

int[] range = {0,1,2,3,4,5,6,7,8,9};
for (int j : range) {
system.out.writeln(j);
if (true) {
j += 2;
system.out.writeln("iterno" + j);
}
}

If I remember Java correctly...

Guest
Posts: n/a

 05-13-2007
On May 13, 12:13 am, (E-Mail Removed) (Alex Martelli) wrote:

> As somebody else alredy pointed out, the lambda is supererogatory (to
> say the least).

What a wonderful new word!
I did not know what supererogatory meant, and hoped it had nothing to
do with Eros
Answers.com gave me a meaning synonymous with superfluous, which
I think is what was meant here, but Chambers gave a wonderful
definition where they say it is from the RC Church practice of doing
more
devotions than are necessary so they can be 'banked' for distribution
to others (I suspect, that in the past it may have been for a fee or
a
favour).

Supererogatory, my word of the day.

P.S; http://www.chambersharrap.co.uk/cham...ry+&title=21st

Alex Martelli
Guest
Posts: n/a

 05-13-2007

> On May 13, 12:13 am, (E-Mail Removed) (Alex Martelli) wrote:
>
> > As somebody else alredy pointed out, the lambda is supererogatory (to
> > say the least).

>
> What a wonderful new word!
> I did not know what supererogatory meant, and hoped it had nothing to
> do with Eros
> Answers.com gave me a meaning synonymous with superfluous, which
> I think is what was meant here,

Kind of, yes, cfr <http://www.bartleby.com/61/60/S0896000.html> .

> but Chambers gave a wonderful
> definition where they say it is from the RC Church practice of doing
> more
> devotions than are necessary so they can be 'banked' for distribution
> to others (I suspect, that in the past it may have been for a fee or
> a favour).

"Doing more than necessary" may be wonderful in a devotional context,
but not necessarily in an engineering one (cfr also, for a slightly
different slant on "do just what's needed",
<http://en.wikipedia.org/wiki/You_Ain't_Gonna_Need_It>).

> Supererogatory, my word of the day.

Alex

Cesar G. Miguel
Guest
Posts: n/a

 05-13-2007
On May 12, 8:13 pm, (E-Mail Removed) (Alex Martelli) wrote:
> Cesar G. Miguel <(E-Mail Removed)> wrote:
>
> > On May 12, 3:40 pm, Dmitry Dzhus <(E-Mail Removed)> wrote:
> > > > Actually I'm trying to convert a string to a list of float numbers:
> > > > str = '53,20,4,2' to L = [53.0, 20.0, 4.0, 2.0]

>
> > > str="53,20,4,2"
> > > map(lambda s: float(s), str.split(','))

>
> > > Last expression returns: [53.0, 20.0, 4.0, 2.0]
> > > --
> > > Happy Hacking.

>
> > > Dmitry "Sphinx" Dzhushttp://sphinx.net.ru

>
> > Nice!

>
> As somebody else alredy pointed out, the lambda is supererogatory (to
> say the least).
>
> > The following also works using split and list comprehension (as
> > suggested in a brazilian python forum):

>
> > -------------------
> > L = []
> > file = ['5,1378,1,9', '2,1,4,5']
> > str=''
> > for item in file:
> > L.append([float(n) for n in item.split(',')])

>
> The assignment to str is useless (in fact potentially damaging because
> you're hiding a built-in name).
>
> L = [float(n) for item in file for n in item.split(',')]
>
> is what I'd call Pythonic, personally (yes, the two for clauses need to
> be in this order, that of their nesting).
>
> Alex

Yes, 'str' is unnecessary. I just forgot to remove it from the code.