Patch : doct.merge

[Nicolas Lehuen]

Hi,

I've posted this patch on Source forge :

http://sourceforge.net/tracker/index.php?func=detail&aid=1391204&group_id=5470&atid=305470

If you want to update a dictionary with another one, you can simply use
update :

a = dict(a=1,c=3)
b = dict(a=0,b=2)
a.update(b)
assert a == dict(a=0,b=2,c=3)

However, sometimes you want to merge the second dict into the first,
all while keeping the values that are already defined in the first.
This is useful if you want to insert default values in the dictionary
without overriding what is already defined.

Currently this can be done in a few different ways, but all are awkward
and/or inefficient :

a = dict(a=1,c=3)
b = dict(a=0,b=2)

Method 1:
for k in b:
    if k not in a:
        a[k] = b[k]

Method 2:
temp = dict(b)
temp.update(a)
a = temp

This patch adds a merge() method to the dict object, with the same
signature and usage as the update() method. Under the hood, it simply
uses PyDict_Merge() with the override parameter set to 0 instead of 1.
There's nothing new, therefore : the C API already provides this
functionality (though it is not used in the dictobject.c scope), so why
not expose it ? The result is :

a = dict(a=1,c=3)
b = dict(a=0,b=2)
a.merge(b)
assert a == dict(a=1,b=2,c=3)

Does this seem a good idea to you guys ?

Regards,
Nicolas