Finding if a path exists within a json in python

Question

So I am trying to work with an api currently which returns json data such as:

 {
    "emp1" : {
      "EmpName" : "Chris Jackman",
      "EmpAge" : "34",
      "EmpGender" : "Male",
      "EmpDept" : "IT",
      "EmpDesg" : "Project Manager"
      "EmpSal": {
                  "2019": 20000
                  "2020": 23000
 },

    "emp2" : {
      "EmpName" : "Mary Jane",
      "EmpAge" : "27",
      "EmpGender" : "Female",
      "EmpDept" : "IT"
  }
}

Occasionally when we query the API one of these fields will be missing. When we try to access it

my_var = my_json["emp2"]["EmpDesg"]

Which will return a key error:

data_dict["EmpDesg"] = my_json["emp2"]["EmpDesg"]
KeyError: 'EmpDesg'

Is there a way to neatly deal with json paths missing rather than wrapping each field in a try catch:

    try:
        data_dict["EmpName"] = my_json["emp1"]["EmpName"]
    except KeyError as e:
        data_dict["EmpName"] = ""

    try:
        data_dict["EmpAge"] = my_json["emp1"]["EmpAge"]
    except KeyError as e:
        data_dict["EmpAge"] = ""

    try:
        data_dict["EmpGender"] = my_json["emp1"]["EmpGender"]
    except KeyError as e:
        data_dict["EmpGender"] = ""

    try:
        data_dict["salary"] = my_json["emp1"]["EmpSal"]["2020"]
    except KeyError as e:
        data_dict["salary"] = ""

OneCricketeer · Accepted Answer · 2021-07-29 17:19:29Z

1

If you want to check if a key exists, use "key" in data, not a try, except KeyError

Otherwise, if all you want is a default when a key doesn't exist, use .get() with the default parameter

emp1 = my_json["emp1"]
data_dict = {
  "EmpName": emp1.get("EmpName", '')
  "EmpAge": emp1.get("EmpAge", '')
}

Or

keys = ['EmpName', 'EmpAge']
data_dict = {k: emp1.get(k, '') for k in keys}

answered Jul 29, 2021 at 17:19

OneCricketeer

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THK · Accepted Answer · 2021-07-29 17:33:55Z

0

To check if a path of arbitrary length exists in a given dict:

def path_exists(d, path) -> bool:
    """Return True if path exists in given dict."""
    next = d
    while path:
        k = path.pop(0)
        if k in next:
            next = next[k]
        else:
            return False

    return True

For example:


In [4]: path_exists(d, ['emp1', 'EmpName'])
Out[4]: True

In [5]: path_exists(d, ['emp1', 'EmpSal', '2019'])
Out[5]: True

In [6]: path_exists(d, ['emp1', 'EmpSal', '2018'])
Out[6]: False

So you can check whether the path exists (just once) before confidently traversing the dict.

answered Jul 29, 2021 at 17:33

THK

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