Efficient way to remove keys with empty strings from a dict

Question

I have a dict and would like to remove all the keys for which there are empty value strings.

metadata = {u\'Composite:PreviewImage\': u\'(Binary data 101973          


        

Answer 1

Quick Answer (TL;DR)

Example01

### example01 -------------------

mydict  =   { "alpha":0,
              "bravo":"0",
              "charlie":"three",
              "delta":[],
              "echo":False,
              "foxy":"False",
              "golf":"",
              "hotel":"   ",                        
            }
newdict =   dict([(vkey, vdata) for vkey, vdata in mydict.iteritems() if(vdata) ])
print newdict

### result01 -------------------
result01 ='''
{'foxy': 'False', 'charlie': 'three', 'bravo': '0'}
'''

Detailed Answer

Problem

• Context: Python 2.x
• Scenario: Developer wishes modify a dictionary to exclude blank values
  • aka remove empty values from a dictionary
  • aka delete keys with blank values
  • aka filter dictionary for non-blank values over each key-value pair

Solution

• example01 use python list-comprehension syntax with simple conditional to remove "empty" values

Pitfalls

• example01 only operates on a copy of the original dictionary (does not modify in place)
• example01 may produce unexpected results depending on what developer means by "empty"
  • Does developer mean to keep values that are falsy?
  • If the values in the dictionary are not gauranteed to be strings, developer may have unexpected data loss.
  • result01 shows that only three key-value pairs were preserved from the original set

Alternate example

• example02 helps deal with potential pitfalls
• The approach is to use a more precise definition of "empty" by changing the conditional.
• Here we only want to filter out values that evaluate to blank strings.
• Here we also use .strip() to filter out values that consist of only whitespace.

Example02

### example02 -------------------

mydict  =   { "alpha":0,
              "bravo":"0",
              "charlie":"three",
              "delta":[],
              "echo":False,
              "foxy":"False",
              "golf":"",
              "hotel":"   ",
            }
newdict =   dict([(vkey, vdata) for vkey, vdata in mydict.iteritems() if(str(vdata).strip()) ])
print newdict

### result02 -------------------
result02 ='''
{'alpha': 0,
  'bravo': '0', 
  'charlie': 'three', 
  'delta': [],
  'echo': False,
  'foxy': 'False'
  }
'''

See also

• list-comprehension
• falsy
• checking for empty string
• modifying original dictionary in place
• dictionary comprehensions
• pitfalls of checking for empty string