Plotting Horizontal Bars

In this post we will review how to plot horizontal bars using MatPlot

Let’s put the code first

import matplotlib.pyplot as plt


plt.barh(items,sale_units,color="green",label="Sales by Cat")
plt.xlabel("Sales Units")
plt.ylabel("Sales Category")
plt.text(500,1,"Price Dropped",fontsize=14, color="blue")
plt.text(100,3,"Stock Issue",fontsize=14, color="red")
plt.title("Sales by Category")

As you can see we can establish the size of the figure and adjust the size of the figure we the command plt.figure(figsize=(X,Y))

To draw horizontal bars we use the command plt.barh()

One interesting thing is the possibility to add specific comment to the plot area to facilitate the understanding from the user.

We can achieve that using the command plt.text where we first establish the position of the command, then the text we want to show and then we can format the text by specifying font size and color.

Plotting Vertical Bars

Let’s have a look at how to Plot Vertical Bars using MatPlot Lib

In this example we imagine that we have to represent the sales of 4 categories of items: “Radio”,”Television”,”Phones”,”PlayStation”

We also know that each of this categories has sold respectively : 400,100,200,600 units.

Let’s have a look at the code:

import matplotlib.pyplot as plt
sale_units=[400,100,200,600],sale_units,color="blue",label="Units by Cat")
plt.title("Sales by Category")
plt.xlabel("Category of Goods")
plt.ylabel("Unit Sales")

As you can see in line 4 we represent categories of item (Axis X) and sale units (Axis Y). We also add that the label that describes better the content of the graph.

As we have defined a label we can now implement a new function (plt.legend). This function needs as a parameter represented by the location. Right now in this example we will tell the program to put the legend into the best location.

Finally we show the graph calling the function

MatPlot Library

In this section we will look at how to plot series using Matplot Library.

Let’s suppose that we have a series with the following value : 200,400,600,800,800.

Those values relates to the month 2 (Feb), 4 (Apr), 6 (June), 8 (Aug) and 10 (Oct)

We want to represent the series using MatPlot.

Below the code that we have to write:

import matplotlib.pyplot as plt
plt.ylabel("Spent USD")
plt.title("Representing a Series of Data")

As you can see we define a plot which will contain the X and Y respectively

We can set the label using the command plt.xlabel(“some text”) or pltylabel(“some text”).

If we want to add a tile the command to use is plt.title(“Add your title here”)

Finally we show the plot with the command

Ok we have plotted a line but what happens if we need to plot more lines and we need to put a legend and we want to format the lines in a different manner?

Let’s have a look at a more complicated example

import matplotlib.pyplot as plt

plt.ylabel("Units Sold")

plt.title("Representing a Series of Data")

As you can see now we have two lines and a legend providing more information.

In comparison with the previous graph we have

  1. Added a sencond line
  2. Format the data choosing a different color for each line
  3. Chose a different style for each line

To format the line we have used a format string. Here is the link to the MatPlot WebPage which contains very useful information


Python Page – List of Posts

GUI Python Projects

This section is about using PyQT in order to design GUI application.

Encryption GUI App

PyQt Calculator Application Part 1

MatPlot Lib Tutorial

In this section we will be looking at how to use MatPlot to plot data and produce graphs for data analysis.

1: Plot series

2. Plot Vertical Bars

3. Plot Horizontal Bars

4. Plot Pie Charts

Project 1: PyQt – A small Calculator – Part 1

In this post we are going to create a small PyQt calculator application. Creating a calculator is always fun. So let’s start.

First of all I have used QT Designer to create the GUI that we need. Here below is the elements included in the GUI:

Qt Design – Our mycalc.ui file

As you can see we are using a gridLayout and adding 5 X 4 matrix of buttons for the very basic operations.

The button of Zero is called “p0”, the button 1 is called “p1” and so on.

The only control that is not a button is the “screen” that is in fact is a QPlainTextEdit called…..screen.

It is important to notice that the window is called calc.

Let’s save the file a mycalc.ui.

Now that we have a QT GUI file (mycalc.ui) we need to run from terminal the command to translate to Python code:

pyuic5 -x mycalc.ui -o

After running this command you will have a new file “”

If you open the file in the terminal you will see that it contains the main components in Python as show below :

The object name is “calc”. Buttons are listed together with the other control.

Python file for our small Calculator App

The file however does not do much : if you run it you will see the GUI application appearing on your screen however the application will not respond to the user inputs.If you press a button nothing will happen.

In order to have a real application responding to the user inputs we need to write another Python file. Of course the Python file is “interfaced” with the file. In other words one has all the controls in our GUI ( while the second one will determine what happens when one of these controls is activated (for example by clicking a button)

So let’s start coding a brand new open file.

We can start with a new class “MainWindow”.

class MainWindow(QMainWindow):

        def __init__(self,va1):
                super(MainWindow, self).__init__()
                self.ui = Ui_calc()

Apart from the va1 addition the rest of the line above are start for a MainWindow Application .

The class MainWindow will retrieve the elements of the UI_calc() class.

Other important part of the template is the bottom part which will launch the application:

app = QApplication(sys.argv)
w = MainWindow("")

Now that the template is set up we can actually start coding our application.

The first thing that we want to achieve is to connect each button with an event that will call in turn a function to show something (a number) in the screen: in other words if the user press the button p0 we want to display zero on the screen and therefore we will need to create a function to do so.

One way of doing this is by coding each button and associate buttons to an event (clicked) and connect it with a function specific function as shown below:

Coding each single control can be a very long and time consuming tak

One alternative approach is to use a for loop cycle to cycle through each button, associate it with an event clicked and connect it with the function.

In order to loop in the Main Window class we need to call a button that is part of the Ui_calc class.

Therefore we need to open the and add two list of buttons as shown below (one list for buttons 0-9 , the other one for all other buttons (+,-*,/, etc)

Creating 2 list of buttons in order to loop though the Main Application

The class Ui_calc has already each of these buttons as element of the class. The only thing we are doing is adding a variable called btn (type list) which included all the button from 0 to 9.

The same thing happens for the button sum,deduct, multiply, backwards,equal, point and cancel which are included a list called o.

So now because these buttons are part of the we can use them in our Python file to implement the loop

// This is a list of functions to display number 0-9

// This is another list of functions to do math operations

//First loop for button 0-9
for x in range(0,10):                     self.ui.btn[x].clicked.connect(self.inputNumber[x])
self.ui.btn[x].setStyleSheet(open('/home/piemex/Documents/Python/GUI/Calc Project/mystylesheet.css').read())

//Second loop for buttons for math operation
for x in range(0,8):
self.ui.o[x].setStyleSheet(open('/home/piemex/Documents/Python/GUI/Calc Project/mystylesheet.css').read())

//Set up a on/off button to start/shut down application
self.ui.ponoff.setStyleSheet(open('/home/piemex/Documents/Python/GUI/Calc Project/mystylesheet.css').read())

//Set Up Screen
self.ui.screen.setStyleSheet(open('/home/piemex/Documents/Python/GUI/Calc Project/mystylesheet.css').read())

In the code above we define a list (inputNumber) that is a collection of functions that we will use when buttons 0-9 are pressed. Each element of the list will activate its own function. So function zero will output zero on the calculator screen.

If the user press one button between 0-9 a corresponding button will be associate from the btn list of buttons that we have defined before.

Here is a comparison of declaring specfically each single button and looping through the list of buttons

A) self.ui.p4.clicked.connect(self.four)

B) self.ui.btn[x].clicked.connect(self.inputNumber[x])

inputNumber[x] is a list of functions : so if a press 4 the number 4 will be passed to the list inputNumber and retrive the funcion associated with that key

With the loop we are much more efficient because all we need is to put a number to the btn list rather than writing each single line.

We repeat the same operation for all buttons associated to a math operation (+,-,*,/ etc) in the second loop.

Let’s check the result once we run the application

Now that we have customize GUI with buttons that call an event we can describe better what happens if we press one button (for example five): in this file the function . So for example let’s say the user wants to multiply 125 * 2. He has already pressed 1 and then 2 and now press the button 5 or key the number five on the keppad. The corresponding function (five) will be called

def five(self):
                 self.va1= self.va1 + "5"

First the function findme will be called.

This function will look at the string in the screen and store it in the variable x. The the string will be searched for an equal sign. If this string includes the sign “= ” the variable y will be greater than -1. That means that an operation has already done previously and that we need to clear the screen and set out variable va1 equal to empty string.

def findme(self):
                if y>-1:

Let’s go back to our five function and suppose that we have do not have any equal sign in the string shown in the screen (so we have not yet told the calculator the whole operation) : in that case the current output shown in the screen will be contacted with the char 5. So we we had pressed 1 and 2 and then we press five the screen will show 125.

Now that we have 125 shown in our screen we want to multiply for 2 for example. So first we press the button multiply which will call the function multiply

def multiply(self):
                self.va1= self.va1 + "*"

The logic of each operator function (+,-,* and /) is a bit the same. The current string shown in the screen (va1) will be contacted with the operator sign and the output shown in the screen with the function screenme.

Now what happens when the equal operator is pressed?

Let’s check it out.

 def equal(self):
                result = 0
                result = eval(self.va1)
                self.ui.screen.insertPlainText("=" + str(result))

We set a variable result equal to zero. We use the eval function to evaluate the string 125* 2. This will return 250.

We move the cursor of the screen to the end and add the equal sign and then we convert the result to string. Finally we move the cursors to the end of the string again.

So now the screen will show 125*2 = 25

I will not describe each single function as at the bottom of the page you will find the link of the whole program.

One interesting aspect is that we want the calculator to work whether the user press with the mouse the button or key the number in the number keypad of the keyboard.

To do so we need to implement a function that listen to key being pressed on the keyboard

       def keyPressEvent(self,e):
                if e.key()==QtCore.Qt.Key_0:

In the above example the code of what happens when the user press zero. As you can see the function zero will be called.

Hope you have enjoyed this little tutorial on Python and QT.

Here is the full program available



Here a little program in Python to Encrypt your message

The program will reverse the string that the user is providing.

To reverse the string the program will use the ASCII Table.

The program will:

  1. Convert all chars to lower case
  2. Initiate a loop in the string
  3. For each char that is different from a separator (” “)
  4. Convert the char character to ASCII code
  5. Calculate the differential between the ASCII Code of the Character and the ASCII Code 97 (letter a)
  6. Substract from 122 (letter z) the different al in the previous point
  7. Build the String by concatenating each char

Here is the code:

Python Code – Simple Encrypting Program

a=input("Please give me a string")
for x in a:
    if (x!=" "):
             mys=mys+" "


Here is a small version of the Program using QT interface