Don't surprise the programmer by behaving/working differently than expected.
Questions tagged [least-astonishment]
15 questions
3352
votes
34 answers
"Least Astonishment" and the Mutable Default Argument
Anyone tinkering with Python long enough has been bitten (or torn to pieces) by the following issue:
def foo(a=[]):
a.append(5)
return a
Python novices would expect this function called with no parameter to always return a list with only…
Stefano Borini
- 138,652
- 96
- 297
- 431
34
votes
3 answers
Why is negative id or zero considered a bad practice?
Why is negative id or zero considered a bad practice when inserting a primary key in a database table?
I think it could be useful in some cases, but people say that it is not recommended, despite the fact that they never say/know why.
So, I was…
falsarella
- 12,217
- 9
- 69
- 115
12
votes
5 answers
"Boolean" operations in Python (ie: the and/or operators)
This method searches for the first group of word characters (ie: [a-zA-Z0-9_]), returning the first matched group or None in case of failure.
def test(str):
m = re.search(r'(\w+)', str)
if m:
return m.group(1)
return None
The…
NullUserException
- 83,810
- 28
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7
votes
2 answers
Reason for allowing Special Characters in Python Attributes
I somewhat accidentally discovered that you can set 'illegal' attributes to an object using setattr. By illegal, I mean attributes with names that can't be retrieve using the __getattr__ interface with traditional . operator references. They can…
Keozon
- 998
- 10
- 25
7
votes
1 answer
Shouldn't using FieldInfo.SetValue to set a ValueType to null fail?
(related to PropertyInfo SetValue and nulls)
If I have public class Thing { public int X; }, a Thing o, and a FieldInfo fi that points to the X field, why is it legal to call fi.SetValue(o, null)? The runtime sets the field X to zero, i.e.…
Sebastian Good
- 6,310
- 2
- 33
- 57
5
votes
1 answer
Default function values in multi-layer architecture
Wondering the best way to set defaults in a multi-layer application structure. Specifically, if a certain work flow requires a nested set of function calls, is the default specified on all the functions, or just on the top level function and passed…
Clay Wardell
- 14,846
- 13
- 44
- 65
3
votes
2 answers
Make ++o++ complain for types with user defined pre- and postfix increment operators
I'm looking for a way to prevent ++x++ from working for types with user defined prefix and postfix increment operators.
For builtin types the result type of the postfix operator is not an lvalue but a prvalue expression and the compilers complain…
jesses
- 559
- 3
- 15
2
votes
1 answer
Oddly Ruby behavior
I need to check if a variable is an array, and if not convert it into one before proceed with further processing. So, my code looks like this:
class Test < Struct.new(:args)
def eval
p "1. #{args}"
args = (args.instance_of?…
cheng81
- 2,434
- 2
- 21
- 18
2
votes
1 answer
Collection initializers inside object initializers with default values
I just stumbled upon the following issue:
class Settings
{
// Let's set some default value: { 1 }
public ICollection AllowedIds = new List() { 1 };
}
static void Main(string[] args)
{
var s = new Settings
{
…
Heinzi
- 167,459
- 57
- 363
- 519
2
votes
1 answer
Returning `self` at ActiveRecord class method loses indirect reference
When defining a class method at an ActiveRecord, if I return self, the indirect reference is lost.
I'm not sure if I am using the right vocabulary, as I am just learning Ruby on Rails, so here is an example:
class User < ActiveRecord::Base
…
Thiago Negri
- 5,221
- 2
- 28
- 39
1
vote
1 answer
Should I give the backing beans another name than the class?
Should I give the backing beans a new name in the @Named annotation, or should I use the same as the class for readability? Are there any guidelines on when to not or when to do this?
I have a backing bean that provides a dropdown component with…
user626912
- 2,546
- 3
- 24
- 33
0
votes
0 answers
“Never alter or delete a user’s work without them knowing” - is there a name for this software design principle?
Is there a software design principle that says an application should never alter or delete a user’s work done in the application without them knowing?
It’s very similar to the Principle of Least Astonishment, but specifically referring to modifying…
user3163495
- 2,425
- 2
- 26
- 43
0
votes
0 answers
Mutable vs immutable object behavior in python functions
the two pieces of code below produce different outputs.
def f1(x= []):
x.append(1)
return x
print(f1())
print(f1())
Output is:
[1]
[1, 1]
And for the second function:
def f2(x=0):
x+=1
return x
print(f2())
print(f2())
Output…
ste_kwr
- 820
- 1
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- 21
0
votes
0 answers
Prevent conversion to factor when number of columns in a data.frame can be reduced to one
I have a procedure that can extract items from a data frame based on a list of conditions on the columns (see Extracting items from an R data frame using criteria given as a (column_name = value) list):
Here are the data frame and condition list:
>…
bli
- 7,549
- 7
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- 94
0
votes
3 answers
Recurring dates on dates that do not exist
When giving the option for something to reoccur every certain amount of time how should I treat times that don't reoccur on every interval?
For example what should happen to birthday reminders for February 29th? Or if I have a monthly appointment on…
Motti
- 110,860
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- 262