Assertion in list comprehension

[beginner]

Hi,

Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.

I just wish I could put the assertions into list comprehensions.

x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]

#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

Thanks,
Geoffrey

[danmcleran@yahoo.com]

Re: Assertion in list comprehension

On Aug 1, 9:37 am, beginner <zyzhu2...@gmai l.comwrote:

Hi,
>
Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.
>
I just wish I could put the assertions into list comprehensions.
>
x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]
>
#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)
>
Thanks,
Geoffrey

Can't you just call a function from within your list comprehension and
do whatever you want for each item? Something like this (not tested):

def checker(item):
assert(len(item ) <= 2 and len(item) 0)
if len(item) == 2:
assert(item[0].c == "C" and item[1].c == "P"

return len(item) == 2

x = [whatever for item in all_items if checker(item = item)]

[beginner]

Re: Assertion in list comprehension

On Aug 1, 11:09 am, "danmcle...@yah oo.com" <danmcle...@yah oo.com>
wrote:

On Aug 1, 9:37 am, beginner <zyzhu2...@gmai l.comwrote:
>
>
>
>
>

Hi,

>

Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.

>

I just wish I could put the assertions into list comprehensions.

>

x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]

>

#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

>

Thanks,
Geoffrey

>
Can't you just call a function from within your list comprehension and
do whatever you want for each item? Something like this (not tested):
>
def checker(item):
assert(len(item ) <= 2 and len(item) 0)
if len(item) == 2:
assert(item[0].c == "C" and item[1].c == "P"
>
return len(item) == 2
>
x = [whatever for item in all_items if checker(item = item)]- Hide quoted text -
>
- Show quoted text -

Good idea! Thank you!

[Chris Mellon]

Re: Assertion in list comprehension

On 8/1/07, beginner <zyzhu2000@gmai l.comwrote:

Hi,
>
Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.
>
I just wish I could put the assertions into list comprehensions.
>
x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]
>
#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy
to accidentally write ones that always pass this way.

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

[Stargaming]

Re: Assertion in list comprehension

On Wed, 01 Aug 2007 11:28:48 -0500, Chris Mellon wrote:

On 8/1/07, beginner <zyzhu2000@gmai l.comwrote:

>Hi,
>>
>Does anyone know how to put an assertion in list comprehension? I have
>the following list comprehension, but I want to use an assertion to
>check the contents of rec_stdl. I ended up using another loop which
>essentially duplicates the functions of list comprehension. It just
>look like a waste of coding and computer time to me.
>>
>I just wish I could put the assertions into list comprehensions.
>>
> x=[(rec_stdl[0].st/10000.0,
> rec_stdl[0].cl,
> rec_stdl[0].bb,
> rec_stdl[0].bo,
> rec_stdl[1].bb,
> rec_stdl[1].bo,
> rec_stdl[0].ex
> )
> for rec_stdl in rec_by_ex if len(rec_stdl)== 2
> ]
>>
> #duplicated loop
> if __debug__:
> for rec_stdl in rec_by_ex:
> l=len(rec_stdl)
> assert(l<=2 and l>0)
> if l==2:
> assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
> assert(rec_stdl[0].ex==rec_stdl[1].ex)
> assert(rec_stdl[0].st==rec_stdl[1].st)
> assert(rec_stdl[0].cp==rec_stdl[1].cp)

>
First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy to
accidentally write ones that always pass this way.

Could you come up with an example? I can only think of accidentally
injecting a comma, what would create a (true, in a boolean context) tuple.

And, well, if you're only using () for readabilty, this might sometimes
look messy when calling assert with the extended syntax::

assert(False), "error text"

Where one could expect the construction of a tuple.

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

Well, the `assert` isn't there for no reason, but if you're serious about
it, `raise` could be better.

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

Huh? What beginner is doing there seems more like input validation than
testing. Unit or doctests are meant for testing (and in case of doctests,
showing) whether a function works as expected.

[Marc 'BlackJack' Rintsch]

Re: Assertion in list comprehension

On Wed, 01 Aug 2007 16:55:53 +0000, Stargaming wrote:

>Thirdly: This sort of testing is precisely what unit tests and/or
>doctests are for.

>
Huh? What beginner is doing there seems more like input validation than
testing. Unit or doctests are meant for testing (and in case of doctests,
showing) whether a function works as expected.

If it is input validation I wouldn't expect it protected by a ``if
__debug__:``. That looks more like debugging/testing.

Ciao,
Marc 'BlackJack' Rintsch

[beginner]

Re: Assertion in list comprehension

On Aug 1, 11:28 am, "Chris Mellon" <arka...@gmail. comwrote:

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:
>
>
>
>
>

Hi,

>

Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.

>

I just wish I could put the assertions into list comprehensions.

>

x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]

>

#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

>
First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy
to accidentally write ones that always pass this way.

Do you mean I should not use the parentheses?

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

I know. My original question was how. Dan suggested to write a checker
function.

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

Agreed.

[Chris Mellon]

Re: Assertion in list comprehension

On 8/1/07, beginner <zyzhu2000@gmai l.comwrote:

On Aug 1, 11:28 am, "Chris Mellon" <arka...@gmail. comwrote:

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:

Hi,

Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.

I just wish I could put the assertions into list comprehensions.

x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]

#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy
to accidentally write ones that always pass this way.

>
>
Do you mean I should not use the parentheses?
>

Yes.

>

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

>
I know. My original question was how. Dan suggested to write a checker
function.
>

Use the second block in all cases. In any situation where "if
__debug__" is False, the asserts are a noop and in fact won't even be
present in the bytecode.

>

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

>
Agreed.
>
--

http://mail.python.org/mailman/listinfo/python-list

>

[Chris Mellon]

Re: Assertion in list comprehension

On 01 Aug 2007 16:55:53 GMT, Stargaming <stargaming@gma il.comwrote:

On Wed, 01 Aug 2007 11:28:48 -0500, Chris Mellon wrote:
>

On 8/1/07, beginner <zyzhu2000@gmai l.comwrote:

Hi,
>
Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.
>
I just wish I could put the assertions into list comprehensions.
>
x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]
>
#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy to
accidentally write ones that always pass this way.

>
Could you come up with an example? I can only think of accidentally
injecting a comma, what would create a (true, in a boolean context) tuple.
>
And, well, if you're only using () for readabilty, this might sometimes
look messy when calling assert with the extended syntax::
>
assert(False), "error text"
>

It's very easy to write this as assert(False, "error text") if you're
in the habit of thinking that assert is a function.

Where one could expect the construction of a tuple.
>

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

>
Well, the `assert` isn't there for no reason, but if you're serious about
it, `raise` could be better.
>

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

>
Huh? What beginner is doing there seems more like input validation than
testing. Unit or doctests are meant for testing (and in case of doctests,
showing) whether a function works as expected.

Not in a big __debug__ block it isn't.

--

http://mail.python.org/mailman/listinfo/python-list

>

[beginner]

Re: Assertion in list comprehension

On Aug 1, 12:35 pm, "Chris Mellon" <arka...@gmail. comwrote:

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:
>
>
>
>
>

On Aug 1, 11:28 am, "Chris Mellon" <arka...@gmail. comwrote:

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:

>

Hi,

>

Does anyone know how to put an assertion in list comprehension? I have
the following list comprehension, but I want to use an assertion to
check the contents of rec_stdl. I ended up using another loop which
essentially duplicates the functions of list comprehension. It just
look like a waste of coding and computer time to me.

>

I just wish I could put the assertions into list comprehensions.

>

x=[(rec_stdl[0].st/10000.0,
rec_stdl[0].cl,
rec_stdl[0].bb,
rec_stdl[0].bo,
rec_stdl[1].bb,
rec_stdl[1].bo,
rec_stdl[0].ex
)
for rec_stdl in rec_by_ex if len(rec_stdl)== 2
]

>

#duplicated loop
if __debug__:
for rec_stdl in rec_by_ex:
l=len(rec_stdl)
assert(l<=2 and l>0)
if l==2:
assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
assert(rec_stdl[0].ex==rec_stdl[1].ex)
assert(rec_stdl[0].st==rec_stdl[1].st)
assert(rec_stdl[0].cp==rec_stdl[1].cp)

>

First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy
to accidentally write ones that always pass this way.

>

Do you mean I should not use the parentheses?

>
Yes.
>
>
>

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

>

I know. My original question was how. Dan suggested to write a checker
function.

>
Use the second block in all cases. In any situation where "if
__debug__" is False, the asserts are a noop and in fact won't even be
present in the bytecode.
>
>
>
>
>

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

>

Agreed.

>

--
http://mail.python.org/mailman/listinfo/python-list- Hide quoted text -

>
- Show quoted text -- Hide quoted text -
>
- Show quoted text -

I see. In fact I want to whole block surrounded by __debug__ to be
optimized away in non-debug runs. If the logic of my program is
correct, the asserts are guaranteed to be true, no matter what the
input is. It is not input checking.

[beginner]

Re: Assertion in list comprehension

On Aug 1, 12:38 pm, "Chris Mellon" <arka...@gmail. comwrote:

On 01 Aug 2007 16:55:53 GMT, Stargaming <stargam...@gma il.comwrote:
>
>
>
>
>

On Wed, 01 Aug 2007 11:28:48 -0500, Chris Mellon wrote:

>

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:
>Hi,

>

>Does anyone know how to put an assertion in list comprehension? I have
>the following list comprehension, but I want to use an assertion to
>check the contents of rec_stdl. I ended up using another loop which
>essentially duplicates the functions of list comprehension. It just
>look like a waste of coding and computer time to me.

>

>I just wish I could put the assertions into list comprehensions.

>

> x=[(rec_stdl[0].st/10000.0,
> rec_stdl[0].cl,
> rec_stdl[0].bb,
> rec_stdl[0].bo,
> rec_stdl[1].bb,
> rec_stdl[1].bo,
> rec_stdl[0].ex
> )
> for rec_stdl in rec_by_ex if len(rec_stdl)== 2
> ]

>

> #duplicated loop
> if __debug__:
> for rec_stdl in rec_by_ex:
> l=len(rec_stdl)
> assert(l<=2 and l>0)
> if l==2:
> assert(rec_stdl[0].c=="C" and rec_stdl[1].c=="P")
> assert(rec_stdl[0].ex==rec_stdl[1].ex)
> assert(rec_stdl[0].st==rec_stdl[1].st)
> assert(rec_stdl[0].cp==rec_stdl[1].cp)

>

First: All your asserts are wrong. Assert is a statement, not a
function. These specific ones will behave as expected, but it's easy to
accidentally write ones that always pass this way.

>

Could you come up with an example? I can only think of accidentally
injecting a comma, what would create a (true, in a boolean context) tuple.

>

And, well, if you're only using () for readabilty, this might sometimes
look messy when calling assert with the extended syntax::

>

assert(False), "error text"

>
It's very easy to write this as assert(False, "error text") if you're
in the habit of thinking that assert is a function.
>

Where one could expect the construction of a tuple.

>

Secondly: This is a waste of code, because if __debug__ is not defined
asserts will be skipped by the compiler. You could use the same loop
block for both branches.

>

Well, the `assert` isn't there for no reason, but if you're serious about
it, `raise` could be better.

>

Thirdly: This sort of testing is precisely what unit tests and/or
doctests are for.

>

Huh? What beginner is doing there seems more like input validation than
testing. Unit or doctests are meant for testing (and in case of doctests,
showing) whether a function works as expected.

>
Not in a big __debug__ block it isn't.

No I was trying to test the logic of my code not validating the
contents of the data. Thanks.

>
>

--
http://mail.python.org/mailman/listinfo/python-list- Hide quoted text -

>
- Show quoted text -- Hide quoted text -
>
- Show quoted text -

[Chris Mellon]

Re: Assertion in list comprehension

On 8/1/07, beginner <zyzhu2000@gmai l.comwrote:

On Aug 1, 12:35 pm, "Chris Mellon" <arka...@gmail. comwrote:

On 8/1/07, beginner <zyzhu2...@gmai l.comwrote:

<much snippage>

I see. In fact I want to whole block surrounded by __debug__ to be
optimized away in non-debug runs. If the logic of my program is
correct, the asserts are guaranteed to be true, no matter what the
input is. It is not input checking.
>

I inferred as much. That's why placing it in a unit or doctest is even better.