Autovivification means implicitly creating data structures accessed via name when explicitly creating their data, such as initializing a hash upon assigning the first key/value pair, or creating a folder upon saving a file in a new path.
Questions tagged [autovivification]
75 questions
4
votes
1 answer
perl autovivification when calling subroutine
Why auto-vivification does not work when calling procedures? Is there a way to prohibit it in this case too?
#!/usr/bin/env perl
no autovivification;
use Data::Dumper;
sub testsub { }
my $task;
print Dumper($task); # $VAR1 = undef;
my $a =…
Konstantin Tokar
- 43
- 3
4
votes
3 answers
Unintentionally adding keys to hash while iterating
I'm iterating through a cache of a hash of hashes of latitude keys that point to key/value pairs of longitudes/cities. I'm trying to find approximate matches for latitudes/longitudes that are close enough to what's already been looked up and is in…
ikebukuru
- 89
- 7
4
votes
1 answer
Perl cgi compilation error in autovivication.pm
I'm using a perl cgi script that uses our own libraries, which use the "no autovivification" pragma. E.g.
/usr/lib/company/mysim.cgi:
#!/usr/bin/perl -w
use strict;
# ... other use
use Company::Module1;
/usr/lib/perl5/Company/Module1.pm
package…
HalfOpenedEye
- 41
- 3
4
votes
3 answers
PERL-like autovivification with default value in Python, and returns a default value from non-existing arbitrary nesting?
Suppose I want PERL-like autovivication in Python, i.e.:
>>> d = Autovivifier()
>>> d = ['nested']['key']['value']=10
>>> d
{'nested': {'key': {'value': 10}}}
There are a couple of dominant ways to do that:
Use a recursive default dict
Use a…
dawg
- 98,345
- 23
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4
votes
4 answers
Why does Perl autovivify in this case?
Why does $a become an arrayref? I'm not pushing anything to it.
perl -MData::Dumper -e 'use strict; 1 for @$a; print Dumper $a'
$VAR1 = [];
Eugene Yarmash
- 142,882
- 41
- 325
- 378
3
votes
2 answers
Why does $foo->{bar} autovivify but %$foo doesn't?
I have the following code:
$headers;
some_sub( %$headers );
When I call some_sub I get an error:
Can't use an undefined value as a HASH reference at ...
But similar code does not produce an error:
$headers->{ x };
Why doesn't autovivification…
Eugen Konkov
- 22,193
- 17
- 108
- 158
3
votes
4 answers
How to create nested dictionaries with duplicate keys in python
I want to create data structure with nested dictionaries and duplicate keys. A detailed example is:
data['State1']['Landon']['abc Area'] = 'BOB'
data['State1']['Landon']['abc Area'] = 'SAM'
data['State1']['Landon']['xyz Area'] =…
Aniketan
- 55
- 2
- 9
3
votes
4 answers
Why does Perl's autovivification work in this case?
Can some one help me understand the output of this Perl program:
use Data::Dumper;
my %hash;
$hash{hello} = "foo";
$hash{hello}{world} = "bar";
print $hash{hello} . "\n";
print $hash{hello}{world} . "\n";
print Dumper(\%hash);
And the…
tster
- 17,883
- 5
- 53
- 72
3
votes
5 answers
In Perl, how to use 'defined' function on elements of two-dimensional array?
I am trying to check if an element is defined, using defined function in Perl.
Code :
$mylist[0][0]="wqeqwe";
$mylist[0][1]="afasf";
$mylist[1][0]="lkkjh";
print scalar(@mylist), "\n";
if (defined($mylist[2][0])){print "TRUE\n";}
print…
384X21
- 6,553
- 3
- 17
- 17
2
votes
2 answers
Understanding the difference in behaviour between perl's assign-or operator and the combination of assignment and logical-or operators
Today I was surprised when I came across the following behaviour in perl:
sub f { die if %{ $_[0] }; 42 }
my %h;
$h{x} ||= f(\%h); # we die. $_[0] references a hash with an 'x' key during f's run-time
In contrast, given the same set-up, the…
rafl
- 11,980
- 2
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2
votes
2 answers
perl check nested hash reference
I have the following code:
#!/usr/bin/perl
use warnings;
use strict;
use Data::Dumper;
my $site = "test.com";
my $data = {
"test" => 1
};
my $user = defined($data->{addons}->{$site}->{username}) ? $data->{addons}->{$site}->{username} :…
Zhivko Angelov
- 139
- 2
- 7
2
votes
9 answers
Python: How to update value of key value pair in nested dictionary?
i am trying to make an inversed document index, therefore i need to know from all unique words in a collection in which doc they occur and how often.
i have used this answer in order two create a nested dictionary. The provided solution works fine,…
Jorrit
- 21
- 1
- 2
2
votes
1 answer
Why perl autovivification does not work for ->@* but ->@[0] does?
I may get values by slicing:
($x, $y, $z) = $hash->{ key }->@[0,1,2]
Why I can not to write?
($x, $y, $z) = $hash->{ key }->@*
For second expression in cases when key is not defined in hash I get error:
Can't use an undefined value as an ARRAY…
Eugen Konkov
- 22,193
- 17
- 108
- 158
2
votes
2 answers
Autovivification in PHP
if I have this SQL query:
select substring(id for 2) as key,
yw, count(*)
from pref_money group by yw, key
returning number of users per week and per key:
key | yw | count
-----+---------+-------
VK | 2010-45 | 144
VK | 2010-44 | …
Alexander Farber
- 21,519
- 75
- 241
- 416
2
votes
2 answers
Efficiently get hash entry only if it exists in Perl
I am quite often writing fragments of code like this:
if (exists $myHash->{$key}) {
$value = $myHash->{$key};
}
What I am trying to do is get the value from the hash if the hash has that key in it, and at the same time I want to avoid…
harmic
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