I want to generate a large number of key value pairs to put in my dictionary using a for loop. For example, the dictionary looks like this:
my_dict = dict()
my_dict["r0"] = "tag 0"
my_dict["r1"] = "tag 1"
my_dict["r2"] = "tag 2"
...
Note that both the key and value follows a pattern, i.e., the number increase by 1. Now I cannot do this 1M times and would prefer an automatic way to initialize my dictionary.
The most efficient way to do this is probably with a dict comprehension:
mydict={'r%s'%n : 'tag %s'%n for n in range(10)}
Which is equivalent to:
mydict=dict()
for n in range(10):
mydict.update({'r%s'%n:'tag %s'%n})
... but more efficient. Just change range(10) as necessary.
You could also use .format() formatting instead of percent (C-like) formatting in the dict:
mydict={'r{}'.format(n) : 'tag {}'.format(n) for n in range(10)}
If you are using Python2 replace all the range() functions with xrange() functions
my_dict = dict()
for i in range(0, 1000000):
key = "r{}".format(i)
value = "tag {}".format(i)
my_dict[key] = value
EDIT: As pointed out by others, if you are using python 2 use xrange instead since it is lazy (so more efficient). In Python 3 range does the same thing as xrange in python 2
my_dict = dict()
for i in xrange(1000000):
my_dict["r%s" % i] = "tag %s" % i
my_dict = dict()
for x in range(1000000):
key="r"+str(x)
val="tag " +str(x)
my_dict[key]=val
simple way is to do the following
#using python format strings
keyf = "r{}"
valf = "tag {}"
#dictionary comprehension
a = {keyf.format(i) : valf.format(i) for i in range(5)}
# can modify range to handle 1,000,000 if you wanted
print(a)
{'r0': 'tag 0', 'r1': 'tag 1', 'r2': 'tag 2', 'r3': 'tag 3', 'r4': 'tag 4', 'r5': 'tag 5'}
if you wanted to quickly append this to another dictionary you would use the dictionary equivalent of extend, which is called update.
b = dict{"x":1,"y":2}
b.update(a)
print(b)
{'x': 1, 'y': 2, 'r0': 'tag 0', 'r1': 'tag 1', 'r2': 'tag 2', 'r3': 'tag 3', 'r4': 'tag 4'}
you could also shorten the original comprehension by doing this:
a = {"r{}".format(i) : "tag {}".format(i) for i in range(5)}
You wouldn't even need to make keyf, or valf
Python can build dicts from lists:
$ python2 -c "print dict(map(lambda x: ('r' + str(x), 'tag ' + str(x)), range(10)))"
{'r4': 'tag 4', 'r5': 'tag 5', 'r6': 'tag 6', 'r7': 'tag 7', 'r0': 'tag 0', 'r1': 'tag 1', 'r2': 'tag 2', 'r3': 'tag 3', 'r8': 'tag 8', 'r9': 'tag 9'}
