My dictionary in a JSON file looks like this:
{
'key1':value1
'key2':value2
}
I'm writing a loop where each iteration adds a new key to the dictionary in the file. For example, after one iteration the dictionary in the file looks like this:
{
'key1':value1
'key2':value2
'key3':value3
}
I want to use a method to directly append a new key into the dictionary in the file. I don't want to have to read the file in, change data and write it back out again. Is there any way to do this?
This is a rather crude implementation that assumes that the file ends with } and a newline (which explains the -2):
with open('data.json','rb+') as f:
f.seek(-2,2)
f.write(b"'new_key':new_value\n}\n")
You could do this by finding the final closing curly brace and then using file.seek to go to that position. Then you can write your new values, like this:
with open(path, 'rb+') as f:
s = f.read()
index = s.rfind('}')
f.seek(index)
f.write(',\n[YOUR JSON HERE]\n')
f.write(s[index:])
Note that if your structure is actually a list first, this will need you to use ] instead, but otherwise this should work the same. Also note that depending on whether or not you normally use trailing commas (ie. {a: 1, b: 13, c: 231,}) you might want to ommit the comma I added in the first write command.