How would I insert a key-value pair at a specified location in a python dictionary that was loaded from a YAML document?
For example if a dictionary is:
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}
I wish to insert the element 'Phone':'1234'
before Age, and after Name. This is just an example. The actual dictionary I shall be working on is quite large (parsed YAML file), so deleting and reinserting might be a bit cumbersome(I don't really know).
If I am given a way of inserting into a specified position in an OrderedDict, that would be okay too.
解決方案
On python < 3.7 (or cpython < 3.6), you cannot control the ordering of pairs in a standard dictionary.
If you plan on performing arbitrary insertions often, my suggestion would be to use a list to store keys, and a dict to store values.
mykeys = ['Name', 'Age', 'Class']
mydict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'} # order doesn't matter
k, v = 'Phone', '123-456-7890'
mykeys.insert(mykeys.index('Name')+1, k)
mydict[k] = v
for k in mykeys:
print(f'{k} => {mydict[k]}')
# Name => Zara
# Phone => 123-456-7890
# Age => 7
# Class => First
If you plan on initialising a dictionary with ordering whose contents are not likely to change, you can use the collections.OrderedDict structure which maintains insertion order.
from collections import OrderedDict
data = [('Name', 'Zara'), ('Phone', '1234'), ('Age', 7), ('Class', 'First')]
odict = OrderedDict(data)
odict
# OrderedDict([('Name', 'Zara'),
# ('Phone', '1234'),
# ('Age', 7),
# ('Class', 'First')])
Note that OrderedDict does not support insertion at arbitrary positions (it only remembers the order in which keys are inserted into the dictionary).