Python tutorial python dictionary (Dictionary)

Python Dictionary (Dictionary)

A dictionary is another mutable container model, and can store any type of object, such as another container model.

A dictionary consists of a pair of keys and corresponding values. Dictionaries are also referred to as associative arrays or hash tables. The basic syntax is as follows:

Dict = {' Alice ': ' 2341 ', ' Beth ': ' 9102 ', ' Cecil ': ' 3258 '}

You can also create a dictionary like this:

Dict1 = {' abc ': 456};d ict2 = {' abc ': 123, 98.6:37};

Each key and value is separated by a colon (:), each pair is comma-delimited, each pair is separated by commas, and the whole is placed in curly braces ({}).

The key must be unique, but the value does not have to be.

The value can take any data type, but it must be immutable, such as a string, number, or tuple.

Accessing values in the dictionary

Put the corresponding key into the familiar square brackets, the following example:

#!/usr/bin/python dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}; print "dict[' name ']:", dict[' name '];p rint "dict[' age '):", dict[' age ');

The result of the above example output:

dict[' Name ':  zaradict[' age ':  7

If the data is accessed using a key that is not in the dictionary, the output error is as follows:

#!/usr/bin/python dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}; Print "dict[' Alice ']:", dict[' Alice ');

The result of the above example output:

dict[' Zara ']:traceback (most recent):  File "test.py", line 4, <module>    print "dict[' Alice ']:" , dict[' Alice '; Keyerror: ' Alice '

Modify Dictionary

The way to add new content to a dictionary is to add a new key/value pair, modify or delete an existing key/value pair as follows:

#!/usr/bin/python dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}; Dict[' age '] = 8; # Update existing entrydict[' School '] = "DPS School"; # ADD new entry  print "dict[' age '):", dict[' age '];p rint "dict[' School ']:", dict[' School '];

The result of the above example output:

Dict[' age ':  8dict[' School ':  DPS School

Delete a dictionary element

The ability to delete a single element also clears the dictionary, emptying only one operation.

Show Delete a dictionary with the Del command, as in the following example:

#!/usr/bin/python dict = {' Name ': ' Zara ', ' age ': 7, ' Class ': ' First '}; Del dict[' Name ']; # Delete key is ' Name ' entry dict.clear ();     # Empty dictionary all Entries del dict;        # Delete the dictionary print "dict[' age ']:", dict[' age '];p rint "dict[' School ']:", dict[' School '];

However, this throws an exception because the dictionary no longer exists after Del:

dict[' age ']:traceback (most recent):  File "test.py", line 8, in <module>    print "dict[' age ']:", di Ct[' age ']; TypeError: ' Type ' object is unsubscriptable

Note: The Del () method is also discussed later.

Delete a dictionary element

Properties of Dictionary Keys

A dictionary value can take any Python object without restriction, either as a standard object or as a user-defined one, but not a key.

Two important points to keep in mind:

1) The same key is not allowed to appear two times. When created, if the same key is assigned a value of two times, the latter value is remembered, as in the following instance

#!/usr/bin/python dict = {' name ': ' Zara ', ' age ': 7, ' name ': ' Manni '}; print "dict[' name ']:", dict[' name '];

The result of the above example output:

dict[' Name ']:  Manni

2) The key must be immutable, so it can be used as a number, string or tuple, so the list is not, the following example:

#!/usr/bin/python dict = {[' Name ']: ' Zara ', ' Age ': 7}; print "dict[' name ']:", dict[' name '];

The result of the above example output:

Traceback (most recent):  File "test.py", line 3, <module>    dict = {[' Name ']: ' Zara ', ' age ': 7};t Ypeerror:list Objects is unhashable

Dictionary built-in functions & methods

The Python dictionary contains the following built-in functions:

Serial number

Functions and descriptions

1 cmp (DICT1, DICT2)
Compares two dictionary elements.

2 len (dict)
Calculates the number of dictionary elements, that is, the total number of keys.

3 Str (DICT)
The output dictionary is a printable string representation.

4 Type (variable)
Returns the type of the variable entered and returns the dictionary type if the variable is a dictionary.

The Python dictionary contains the following built-in functions:

Serial number

Functions and descriptions

1 radiansdict.clear ()
Delete all elements in a dictionary

2 radiansdict.copy ()
Returns a shallow copy of a dictionary

3 Radiansdict.fromkeys ()
Create a new dictionary with the keys to the dictionary in sequence seq, Val is the initial value corresponding to all keys in the dictionary

4 Radiansdict.get (key, Default=none)
Returns the value of the specified key if the value does not return the default value in the dictionary

5 Radiansdict.has_key (Key)
Returns False if the key returns true in the dictionary Dict

6 Radiansdict.items ()
Returns an array of traversed (key, value) tuples as a list

7 Radiansdict.keys ()
Returns a dictionary of all keys in a list

8 Radiansdict.setdefault (key, Default=none)
Similar to get (), but if the key does not already exist in the dictionary, the key will be added and the value will be set to default

9 Radiansdict.update (DICT2)
Update the key/value pairs of the dictionary dict2 to the Dict

Ten radiansdict.values ()
Returns all values in the dictionary as a list

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