Is it possible to add a key to a Python dictionary after it has been created? It doesn't seem to have an .add() method.
转载于:https://stackoverflow.com/questions/1024847/add-new-keys-to-a-dictionary
>>> d = {'key':'value'}
>>> print(d)
{'key': 'value'}
>>> d['mynewkey'] = 'mynewvalue'
>>> print(d)
{'mynewkey': 'mynewvalue', 'key': 'value'}
dictionary[key] = value
Yeah, it's pretty easy. Just do the following:
dict["key"] = "value"
>>> x = {1:2}
>>> print x
{1: 2}
>>> x.update({3:4})
>>> print x
{1: 2, 3: 4}
I feel like consolidating info about Python dictionaries:
data = {}
# OR
data = dict()
data = {'a':1,'b':2,'c':3}
# OR
data = dict(a=1, b=2, c=3)
# OR
data = {k: v for k, v in (('a', 1),('b',2),('c',3))}
data['a']=1 # Updates if 'a' exists, else adds 'a'
# OR
data.update({'a':1})
# OR
data.update(dict(a=1))
# OR
data.update(a=1)
data.update({'c':3,'d':4}) # Updates 'c' and adds 'd'
data3 = {}
data3.update(data) # Modifies data3, not data
data3.update(data2) # Modifies data3, not data2
del data[key] # Removes specific element in a dictionary
data.pop(key) # Removes the key & returns the value
data.clear() # Clears entire dictionary
key in data
for key in data: # Iterates just through the keys, ignoring the values
for key, value in d.items(): # Iterates through the pairs
for key in d.keys(): # Iterates just through key, ignoring the values
for value in d.values(): # Iterates just through value, ignoring the keys
data = dict(zip(list_with_keys, list_with_values))
Feel free to add more!
data = {}
data['a'] = 'A'
data['b'] = 'B'
for key, value in data.iteritems():
print "%s-%s" % (key, value)
results in
a-A
b-B
If you want to add a dictionary within a dictionary you can do it this way.
Example: Add a new entry to your dictionary & sub dictionary
dictionary = {}
dictionary["new key"] = "some new entry" # add new dictionary entry
dictionary["dictionary_within_a_dictionary"] = {} # this is required by python
dictionary["dictionary_within_a_dictionary"]["sub_dict"] = {"other" : "dictionary"}
print (dictionary)
Output:
{'new key': 'some new entry', 'dictionary_within_a_dictionary': {'sub_dict': {'other': 'dictionarly'}}}
NOTE: Python requires that you first add a sub
dictionary["dictionary_within_a_dictionary"] = {}
before adding entries.
The orthodox syntax is d[key] = value, but if your keyboard is missing the square bracket keys you could do:
d.__setitem__(key, value)
In fact, defining __getitem__ and __setitem__ methods is how you can make your own class support the square bracket syntax. See http://www.diveintopython.net/object_oriented_framework/special_class_methods.html
you can create one
class myDict(dict):
def __init__(self):
self = dict()
def add(self, key, value):
self[key] = value
## example
myd = myDict()
myd.add('apples',6)
myd.add('bananas',3)
print(myd)
gives
>>>
{'apples': 6, 'bananas': 3}
This popular question addresses functional methods of merging dictionaries a and b.
Here are some of the more straightforward methods (tested in Python 3)...
c = dict( a, **b ) ## see also https://stackoverflow.com/q/2255878
c = dict( list(a.items()) + list(b.items()) )
c = dict( i for d in [a,b] for i in d.items() )
Note: The first method above only works if the keys in b are strings.
To add or modify a single element, the b dictionary would contain only that one element...
c = dict( a, **{'d':'dog'} ) ## returns a dictionary based on 'a'
This is equivalent to...
def functional_dict_add( dictionary, key, value ):
temp = dictionary.copy()
temp[key] = value
return temp
c = functional_dict_add( a, 'd', 'dog' )
This is exactly how I would do it: # fixed data with sapce
data = {}
data['f'] = 'F'
data['c'] = 'C'
for key, value in data.iteritems():
print "%s-%s" % (key, value)
This works for me. Enjoy!
we can add new keys to dictionary by this way:
Dictionary_Name[New_Key_Name] = New_Key_Value
Here is the Example:
# This is my dictionary
my_dict = {'Key1': 'Value1', 'Key2': 'Value2'}
# Now add new key in my dictionary
my_dict['key3'] = 'Value3'
# Print updated dictionary
print my_dict
Output:
{'key3': 'Value3', 'Key2': 'Value2', 'Key1': 'Value1'}
It has a update method which you can use like this:
dict.update({"key" : "value"})
So many answers and still everybody forgot about the strangely named, oddly behaved, and yet still handy dict.setdefault()
This
value = my_dict.setdefault(key, default)
basically just does this:
try:
value = my_dict[key]
except KeyError: # key not found
value = my_dict[key] = default
e.g.
>>> mydict = {'a':1, 'b':2, 'c':3}
>>> mydict.setdefault('d', 4)
4 # returns new value at mydict['d']
>>> print(mydict)
{'a':1, 'b':2, 'c':3, 'd':4} # a new key/value pair was indeed added
# but see what happens when trying it on an existing key...
>>> mydict.setdefault('a', 111)
1 # old value was returned
>>> print(mydict)
{'a':1, 'b':2, 'c':3, 'd':4} # existing key was ignored
Use the subscript assignment operator:
d['x'] = "value"
Don't forget that Python's key can by anything hashable which means bool, int, string even a tuple or any objects hashable.
Let's pretend you want to live in the immutable world and do NOT want to modify the original but want to create a new dict that is the result of adding a new key to the original.
In Python 3.5+ you can do:
params = {'a': 1, 'b': 2}
new_params = {**params, **{'c': 3}}
The Python 2 equivalent is:
params = {'a': 1, 'b': 2}
new_params = dict(params, **{'c': 3})
After either of these:
params is still equal to {'a': 1, 'b': 2}
and
new_params is equal to {'a': 1, 'b': 2, 'c': 3}
There will be times when you don't want to modify the original (you only want the result of adding to the original). I find this a refreshing alternative to the following:
params = {'a': 1, 'b': 2}
new_params = params.copy()
new_params['c'] = 3
or
params = {'a': 1, 'b': 2}
new_params = params.copy()
new_params.update({'c': 3})
Reference: https://stackoverflow.com/a/2255892/514866
I would do it like this. Watch out for the directory[name]=number part.
n = int(raw_input())
directory={}
entry={}
# store the values as if they appear in the stdin
for i in xrange(n):
name, number = raw_input().split()
directory[name]=number
# query the values
while (True):
queryname = (str) (raw_input())
try:
strdisp = queryname + "=" + directory[queryname]
print strdisp
except:
print 'Not found'
If you're not joining two dictionaries, but adding new key-value pairs to a dictionary, then using the subscript notation seems like the best way.
import timeit
timeit.timeit('dictionary = {"karga": 1, "darga": 2}; dictionary.update({"aaa": 123123, "asd": 233})')
>> 0.49582505226135254
timeit.timeit('dictionary = {"karga": 1, "darga": 2}; dictionary["aaa"] = 123123; dictionary["asd"] = 233;')
>> 0.20782899856567383
However, if you'd like to add, for example, thousands of new key-value pairs, you should consider using the update() method.