Python Slots Vs Dict
Difference between DataClass vs NamedTuple vs Object in Python Last Updated: Data Class: Data Class is a type of class that is used to store data without any functionality. How to make tables in Python with Plotly. Import plotly.graphobjects as go values = 'Salaries', 'Office', 'Merchandise', 'Legal', 'TOTALEXPENSES', #1st col 'Lorem ipsum dolor sit amet, tollit discere inermis pri ut. Eos ea iusto timeam, an prima laboramus vim. Id usu aeterno adversarium, summo mollis timeam vel ad', 'Lorem ipsum dolor sit amet, tollit discere inermis pri ut.
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Let’s discuss how to convert Python Dictionary to Pandas Dataframe. We can convert a dictionary to a pandas dataframe by using the pd.DataFrame.fromdict class-method. Example 1: Passing the key value as a list. Dictionary in Python on the other hand is an unordered collection of data values, used to store data values like a map, which unlike other Data Types that hold only single value as an element, Dictionary holds key:value pair. Key-value is provided in the dictionary to make it more optimized.
Python: check if key exists in dictionary (6 Ways) Python: How to copy a dictionary Shallow Copy vs Deep Copy; Python: How to create a list of all the Values in a dictionary? Python Dictionary: update function tutorial & examples; What is a dictionary in python and why do we need it? Pandas: Create Series from dictionary in python.
Python Dict Iterate
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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.
List Vs Dictionary Python
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 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 below in the simple example −
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. Note that an exception is raised because after del dict dictionary does not exist any more −
Note − 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 −
(a) More than one entry per key not allowed. Which means no duplicate key is allowed. When duplicate keys 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. Which 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 & Methods
Python includes the following dictionary functions −
| Sr.No. | Function with Description |
|---|---|
| 1 | cmp(dict1, dict2) Compares elements of both dict. |
| 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 following dictionary methods −
| Sr.No. | Methods with Description |
|---|---|
| 1 | dict.clear() Removes all elements of dictionary dict |
| 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) Returns true if key in dictionary dict, false otherwise |
| 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 |
This page describes the use of signals and slots in Qt for Python.The emphasis is on illustrating the use of so-called new-style signals and slots, although the traditional syntax is also given as a reference.
The main goal of this new-style is to provide a more Pythonic syntax to Python programmers.
- 2New syntax: Signal() and Slot()
Traditional syntax: SIGNAL () and SLOT()
QtCore.SIGNAL() and QtCore.SLOT() macros allow Python to interface with Qt signal and slot delivery mechanisms.This is the old way of using signals and slots.
The example below uses the well known clicked signal from a QPushButton.The connect method has a non python-friendly syntax.It is necessary to inform the object, its signal (via macro) and a slot to be connected to.
New syntax: Signal() and Slot()
The new-style uses a different syntax to create and to connect signals and slots.The previous example could be rewritten as:
Using QtCore.Signal()
Signals can be defined using the QtCore.Signal() class.Python types and C types can be passed as parameters to it.If you need to overload it just pass the types as tuples or lists.
In addition to that, it can receive also a named argument name that defines the signal name.If nothing is passed as name then the new signal will have the same name as the variable that it is being assigned to.
The Examples section below has a collection of examples on the use of QtCore.Signal().
Note: Signals should be defined only within classes inheriting from QObject.This way the signal information is added to the class QMetaObject structure.
Using QtCore.Slot()
Slots are assigned and overloaded using the decorator QtCore.Slot().Again, to define a signature just pass the types like the QtCore.Signal() class.Unlike the Signal() class, to overload a function, you don't pass every variation as tuple or list.Instead, you have to define a new decorator for every different signature.The examples section below will make it clearer.
Another difference is about its keywords.Slot() accepts a name and a result.The result keyword defines the type that will be returned and can be a C or Python type.name behaves the same way as in Signal().If nothing is passed as name then the new slot will have the same name as the function that is being decorated.
Examples
The examples below illustrate how to define and connect signals and slots in PySide2.Both basic connections and more complex examples are given.
- Hello World example: the basic example, showing how to connect a signal to a slot without any parameters.
- Next, some arguments are added. This is a modified Hello World version. Some arguments are added to the slot and a new signal is created.
- Add some overloads. A small modification of the previous example, now with overloaded decorators.
- An example with slot overloads and more complicated signal connections and emissions (note that when passing arguments to a signal you use '[]'):
- An example of an object method emitting a signal:
- An example of a signal emitted from another QThread:
- Signals are runtime objects owned by instances, they are not class attributes: