1 This is a design principle for all mutable data structures in Python. Another thing you might notice is that not all data can be sorted or compared. For instance, None, 'hello', 10 doesn’t sort because integers can’t be compared to strings and None can’t be compared to other types. Also, there are some types that don’t have a. To delete a key, value pair in a dictionary, you can use the del method. A disadvantage is that it gives KeyError if you try to delete a nonexistent key. So, instead of the del statement you can use the pop method. This method takes in the key as the parameter.
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Python dictionary method haskey returns true if a given key is available in the dictionary, otherwise it returns a false. Following is the syntax for haskey method − dict.haskey(key) Parameters. Key − This is the Key to be searched in the dictionary. Return Value.
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Each key is separated from its value by a colon (:), the items are separated by commas, and the whole thing is enclosed in curly braces. An empty dictionary without any items is written with just two curly braces, like this: {}.
Keys are unique within a dictionary while values may not be. The values of a dictionary can be of any type, but the keys must be of an immutable data type such as strings, numbers, or tuples.
Accessing Values in Dictionary
To access dictionary elements, you can use the familiar square brackets along with the key to obtain its value. Following is a simple example −
When the above code is executed, it produces the following result −
If we attempt to access a data item with a key, which is not a part of the dictionary, we get an error as follows −
When the above code is executed, it produces the following result −
Updating Dictionary
You can update a dictionary by adding a new entry or a key-value pair, modifying an existing entry, or deleting an existing entry as shown in a simple example given below.
When the above code is executed, it produces the following result −
Delete Dictionary Elements
You can either remove individual dictionary elements or clear the entire contents of a dictionary. You can also delete entire dictionary in a single operation.
To explicitly remove an entire dictionary, just use the del statement. Following is a simple example −
This produces the following result.
An exception is raised because after del dict, the dictionary does not exist anymore.
Note − The del() method is discussed in subsequent section.
Properties of Dictionary Keys
Dictionary values have no restrictions. They can be any arbitrary Python object, either standard objects or user-defined objects. However, same is not true for the keys.
There are two important points to remember about dictionary keys −
Python Dict Find Key By Value
(a) More than one entry per key is not allowed. This means no duplicate key is allowed. When duplicate keys are encountered during assignment, the last assignment wins. For example −
When the above code is executed, it produces the following result −
(b) Keys must be immutable. This means you can use strings, numbers or tuples as dictionary keys but something like ['key'] is not allowed. Following is a simple example −
When the above code is executed, it produces the following result −
Built-in Dictionary Functions and Methods
Python includes the following dictionary functions −
| Sr.No. | Function & Description |
|---|---|
| 1 | cmp(dict1, dict2) No longer available in Python 3. |
| 2 | len(dict) Gives the total length of the dictionary. This would be equal to the number of items in the dictionary. |
| 3 | str(dict) Produces a printable string representation of a dictionary |
| 4 | type(variable) Returns the type of the passed variable. If passed variable is dictionary, then it would return a dictionary type. |
Python includes the following dictionary methods −
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Python Generator Delete Dict Keys
| Sr.No. | Method & Description |
|---|---|
| 1 | dict.clear() Removes all elements of dictionary dictWin 10 key generator free download. |
| 2 | dict.copy() Returns a shallow copy of dictionary dict |
| 3 | dict.fromkeys() Create a new dictionary with keys from seq and values set to value. |
| 4 | dict.get(key, default=None) For key key, returns value or default if key not in dictionary |
| 5 | dict.has_key(key) Removed, use the in operation instead. |
| 6 | dict.items() Returns a list of dict's (key, value) tuple pairs |
| 7 | dict.keys() Returns list of dictionary dict's keys |
| 8 | dict.setdefault(key, default = None) Similar to get(), but will set dict[key] = default if key is not already in dict |
| 9 | dict.update(dict2) Adds dictionary dict2's key-values pairs to dict |
| 10 | dict.values() Returns list of dictionary dict's values |