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Notes/20250805141906-python_dictionary.org

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+:PROPERTIES:
+:ID:       125c81dc-c14f-4b4d-93c6-0a2b157735ac
+:END:
+#+title: python-dictionary
+#+filetags: :python:notes:
+
+Dictionaries are used to store data values in key:value pairs.
+
+A dictionary is a collection which is ordered*, changeable and do not allow duplicates.
+
+*As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.
+
+Dictionaries are written with curly brackets, and have keys and values:
+
+#+begin_src python
+
+  # Create and print a dictionary:
+    thisdict =	{
+      "brand": "Ford",
+      "model": "Mustang",
+      "year": 1964
+    }
+    print(thisdict)
+
+#+end_src
+
+Iterating:
+
+Iterate through Value
+
+To iterate through all values of a dictionary in Python using .values(), you can employ a for loop, accessing each value sequentially. This method allows you to process or display each individual value in the dictionary without explicitly referencing the corresponding keys.
+
+Example: In this example, we are using the values() method to print all the values present in the dictionary.
+
+#+begin_src python :results output
+
+  # create a python dictionary 
+  d = {"name": "Geeks", "topic": "dict", "task": "iterate"}
+
+  # loop over dict values
+  for val in d.values():
+      print(val)
+#+end_src
+
+Iterate through keys
+
+In Python, just looping through the dictionary provides you its keys. You can also iterate keys of a dictionary using built-in `.keys()` method.
+
+#+begin_src python :results output
+
+  # create a python dictionary 
+  d = {"name": "Geeks", "topic": "dict", "task": "iterate"}
+
+  # default loooping gives keys
+  for keys in d:
+  	print(keys)
+      
+  # looping through keys    
+  for keys in d.keys():
+          print(keys)
+
+#+end_src
+
+Iterate through both keys and values
+
+You can use the built-in items() method to access both keys and items at the same time. items() method returns the view object that contains the key-value pair as tuples.
+
+#+begin_src python :results output
+
+  # create a python dictionary 
+  d = {"name": "Geeks", "topic": "dict", "task": "iterate"}
+
+  # iterating both key and values
+  for key, value in d.items():
+      print(f"{key}: {value}")
+
+#+end_src
+
+Sorting:
+
+Lambda function accesses the key (item[0]) during sorting. It offers flexibility if you want to tweak the sorting logic later.
+
+#+begin_src python :results output
+  import operator
+
+  a = {"Gfg": 5, "is": 7, "Best": 2, "for": 9, "geeks": 8}
+  res = dict(sorted(a.items(), key=lambda item: item[0]))
+  print(res)
+
+#+end_src
+
+#+RESULTS:
+: {'Best': 2, 'Gfg': 5, 'is': 7, 'geeks': 8, 'for': 9}
+
+Explanation: `lambda item: item[0]` sorts the dictionary by the first element of each tuple (the key).
+
+[[id:3bbc6099-0187-4bf2-9282-97e5fa443f72][python-sorted-function]]
+
+[[id:9d534e89-7f0b-494c-bff6-7b3be05b85d1][python-lambda]]