Is there a technic to avoid this bug

[hg]

Hi,

In C/C++ I got used to write an expression like so:

#define TEST 0

if (TEST == value)
{

}

in order to avoid the usual bug:
if (value = TEST)
{

}

In a relatively similar domain, I spent a few hours find this bug:

value == self.Get_Value()
if value == WHATEVER:
do this

instead of
value = self.Get_Value()
if value == WHATEVER:
do this

Is there a way to avoid such a bug with some type of construct ?

Thanks,
hg

[Diez B. Roggisch]

hg wrote:

Hi,

In C/C++ I got used to write an expression like so:

#define TEST 0

if (TEST == value)
{

}

in order to avoid the usual bug:
if (value = TEST)
{

}

In a relatively similar domain, I spent a few hours find this bug:

value == self.Get_Value()
if value == WHATEVER:
do this

instead of
value = self.Get_Value()
if value == WHATEVER:
do this

Is there a way to avoid such a bug with some type of construct ?

No. In a language inherent with sideeffects, there is nothing that should
force you to not write that.

However, it might be that either pychecker or pylint will give you a warning
for such statements.

Diez

[Michele Simionato]

On Feb 27, 1:49 pm, "Diez B. Roggisch" <[e-mail]:

However, it might be that either pychecker or pylint will give you a warning
for such statements.

Yep, pychecker gives a warning "Statement appears to have no effect"

Michele Simionato

[hg]

Michele Simionato wrote:

pychecker

Thanks all ... pydev extension does not however ... will have to install
pychecker also.

hg

[John J. Lee]

"Diez B. Roggisch" <de***@nospam.web.dewrites:

hg wrote:

[...]

In a relatively similar domain, I spent a few hours find this bug:

value == self.Get_Value()
if value == WHATEVER:
do this

instead of
value = self.Get_Value()
if value == WHATEVER:
do this

Is there a way to avoid such a bug with some type of construct ?

No. In a language inherent with sideeffects, there is nothing that should
force you to not write that.

[...]

It's illegal in C#:

// -------- compare.cs ----------
class BadComparison {
static void Main() {
1 == 2;
}
}
// -------- end -----------------

$ mcs compare.cs
compare.cs(3,9): error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement
Compilation failed: 1 error(s), 0 warnings
csharp[0]$
// -------- compare2.cs ----------
class BadComparison {
static void Main() {
bool falsehood = 1 == 2;
}
}
// -------- end -----------------

$ mcs compare2.cs
compare2.cs(3,14): warning CS0219: The variable `falsehood' is assigned but its value is never used
Compilation succeeded - 1 warning(s)
John

[Ben Finney]

hg <[e-mail]:

I spent a few hours find this bug:

value == self.Get_Value()
if value == WHATEVER:
do this

instead of
value = self.Get_Value()
if value == WHATEVER:
do this

Is there a way to avoid such a bug with some type of construct ?

Use pylint to check your code for common mistakes.

<URL:http://www.logilab.org/projects/pylint>

===== bad_assign.py =====
""" Demonstrate a logical error """
value = None

value == 10
if value == 10:
print "Yep"
else:
print "Nope"
=====

$ python ./bad_assign.py
Nope

$ pylint ./bad_assign.py
************* Module bad_assign
C: 2: Invalid name "value" (should match (([A-Z_][A-Z1-9_]*)|(__.*__))$)
W: 4: Statement seems to have no effect

[...]

--
\ "When I was crossing the border into Canada, they asked if I |
`\ had any firearms with me. I said, 'Well, what do you need?'" |
_o__) -- Steven Wright |
Ben Finney