{"id":539,"date":"2020-06-04T07:29:00","date_gmt":"2020-06-04T04:29:00","guid":{"rendered":"https:\/\/www.dataplatform.gr\/?p=539"},"modified":"2026-02-24T11:21:04","modified_gmt":"2026-02-24T08:21:04","slug":"python-from-zero-to-hero","status":"publish","type":"post","link":"https:\/\/www.dataplatform.gr\/en\/python-from-zero-to-hero\/","title":{"rendered":"Python from zero to hero"},"content":{"rendered":"

In this not TLDR article (I hope) we will go over all the basic concepts and constructs of the Python scripting programming language.<\/p>\n\n\n\n

H Python<\/strong> it is an interpreted language and not compiled which means that the translation of the program into machine language is not done all at once when we choose to compile but you run directly and translate directly from the interpreter per command line. <\/p>\n\n\n\n

Shebang line<\/h5>\n\n\n\n

At sheband line<\/strong> which should be the first line of our code, we declare the path where Python (the interpreter) is installed.<\/p>\n\n\n\n

#!\/usr\/bin\/python3.6<\/pre>\n\n\n\n
Print<\/h5>\n\n\n\n
At Python<\/strong> we define variables without having to declare them with their datatype. With the function print we display either the variable or directly what we have assigned to it.<\/p>\n\n\n\n
a=2+3\nprint(type(a))\nprint(a)\n<\/pre>\n\n\n\n
<class 'int'>\n5\n<\/code><\/pre>\n\n\n\n
When we set to a variable with quote it is defined as string<\/strong>.<\/p>\n\n\n\n
a='2'+'3'\nprint(type(a))\nprint(a)\n<\/pre>\n\n\n\n
<class 'str'>\n23<\/code><\/pre>\n\n\n\n
When we use it print <\/strong>function we can use the parameter sep<\/strong> to separate the data from each other or the end<\/strong> to be added to the end of the line.<\/p>\n\n\n\n
print('0','1','2','3',sep='-')\nprint('0','1','2','3',end='-')\n<\/pre>\n\n\n\n
0-1-2-3\n0 1 2 3-\n<\/code><\/pre>\n\n\n\n
Loops<\/h5>\n\n\n\n
Let's go to examples of loops with for <\/strong>and while<\/strong>. Don't forget that the range <\/strong>starts at 0 and goes up to the value we set excluding this value.<\/p>\n\n\n\n
for i in range(0,3):\n    print(i)<\/pre>\n\n\n\n
0\n1\n2<\/code><\/pre>\n\n\n\n
i = 0\nwhile i < 3:\n  print(i)\n  i = i + 1<\/pre>\n\n\n\n
0\n1\n2<\/code><\/pre>\n\n\n\n
Data structures<\/h5>\n\n\n\n
In Python we use 3 structures <\/strong>data lists<\/strong>, tuples <\/strong>and dictionary<\/strong>. We can also use combinations such as lists or a dictionary containing tuples.<\/p>\n\n\n\n
Lists<\/h5>\n\n\n\n
H list<\/strong> is an array of data that allows changes such as sorting, removing or adding data.<\/p>\n\n\n\n
Defined as =[a,b].<\/p>\n\n\n\n
list = ['\u03bc\u03c0\u03b1\u03bd\u03ac\u03bd\u03b1','\u03bc\u03ae\u03bb\u03bf','\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9','\u03c6\u03c1\u03ac\u03bf\u03c5\u03bb\u03b1']\nprint(type(list))\nprint(list)\n<\/pre>\n\n\n\n
<class 'list'>\n['\u03bc\u03c0\u03b1\u03bd\u03ac\u03bd\u03b1', '\u03bc\u03ae\u03bb\u03bf', '\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9', '\u03c6\u03c1\u03ac\u03bf\u03c5\u03bb\u03b1']<\/code><\/pre>\n\n\n\n
We can choose from which value to which we want to fetch with the first value being 0<\/p>\n\n\n\n
print(list[1:3])<\/pre>\n\n\n\n
['\u03bc\u03ae\u03bb\u03bf', '\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9']<\/code><\/pre>\n\n\n\n
We can also bring them in reverse order<\/p>\n\n\n\n
print(list[::-1])<\/pre>\n\n\n\n
['\u03c6\u03c1\u03ac\u03bf\u03c5\u03bb\u03b1', '\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9', '\u03bc\u03ae\u03bb\u03bf', '\u03bc\u03c0\u03b1\u03bd\u03ac\u03bd\u03b1']<\/code><\/pre>\n\n\n\n
We can remove and add data.<\/p>\n\n\n\n
list.append('\u03b1\u03bd\u03b1\u03bd\u03ac\u03c2')\nlist.remove('\u03c6\u03c1\u03ac\u03bf\u03c5\u03bb\u03b1')\nprint(list)<\/pre>\n\n\n\n
['\u03bc\u03c0\u03b1\u03bd\u03ac\u03bd\u03b1', '\u03bc\u03ae\u03bb\u03bf', '\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9', '\u03b1\u03bd\u03b1\u03bd\u03ac\u03c2']<\/code><\/pre>\n\n\n\n
We can put it in alphabetical order.<\/p>\n\n\n\n
list.sort()\nprint(list)<\/pre>\n\n\n\n
['\u03b1\u03ba\u03c4\u03b9\u03bd\u03af\u03b4\u03b9\u03bf', '\u03b1\u03bd\u03b1\u03bd\u03ac\u03c2', '\u03ba\u03b5\u03c1\u03ac\u03c3\u03b9', '\u03bc\u03ae\u03bb\u03bf', '\u03bc\u03c0\u03b1\u03bd\u03ac\u03bd\u03b1', '\u03c3\u03cd\u03ba\u03bf']<\/code><\/pre>\n\n\n\n
Tuples<\/h5>\n\n\n\n
That tuple <\/strong>it is like a list with the difference that it is immutable, i.e. it does not accept changes. <\/p>\n\n\n\n
Defined as = (a,b)<\/p>\n\n\n\n
tuple = (1, 2, 3, '\u03c0\u03b1\u03c0\u03ac\u03ba\u03b9')\nprint(type(tuple))\nprint(tuple)<\/pre>\n\n\n\n
<class 'tuple'>\n(1, 2, 3, '\u03c0\u03b1\u03c0\u03ac\u03ba\u03b9')<\/code><\/pre>\n\n\n\n
Dictionaries<\/h5>\n\n\n\n
That dictionary <\/strong>it is like a list with the difference that its structure is divided into key and value. The key is like the title of the field and must be unique.<\/p>\n\n\n\n
Defined as ={key:value}.<\/p>\n\n\n\n
dictionary = {'onoma':('Stratos','Nikos','Maria'),'epitheto':('Matzouranis','Georgiou','Papa')}\nprint(dictionary)\n<\/pre>\n\n\n\n
{'onoma': ('Stratos', 'Nikos', 'Maria'), 'epitheto': ('Matzouranis', 'Georgiou', 'Papa')}<\/code><\/pre>\n\n\n\n
With the command.key <\/strong>we can see the keys it has.<\/p>\n\n\n\n
print(dictionary.keys())<\/pre>\n\n\n\n
dict_keys(['onoma', 'epitheto'])<\/code><\/pre>\n\n\n\n
We can print all the names belonging to the name key:<\/p>\n\n\n\n
print(dictionary.keys())<\/pre>\n\n\n\n
dict_keys(['onoma', 'epitheto'])<\/code><\/pre>\n\n\n\n
We can print all the names belonging to the name key:<\/p>\n\n\n\n
print(dictionary['onoma'])<\/pre>\n\n\n\n
('Stratos', 'Nikos', 'Maria')<\/code><\/pre>\n\n\n\n
We can only print the third name:<\/p>\n\n\n\n
print(dictionary['onoma'][2])<\/pre>\n\n\n\n
Maria<\/code><\/pre>\n\n\n\n
or all prices:<\/p>\n\n\n\n
print(dictionary.values())<\/pre>\n\n\n\n
dict_values([('Stratos', 'Nikos', 'Maria'), ('Matzouranis', 'Georgiou', 'Papa')])<\/code><\/pre>\n\n\n\n
Create and view a multidimensional array<\/h5>\n\n\n\n
Let's do something more advanced, a 4\u00d73 list printed as a table. To achieve this we should use loops like below:<\/p>\n\n\n\n
z = [\n    [i for i in range(4)] \n         for j in range(3)\n    ]\nfor rows in range(len(z)):\n        for col in range(len(z[0])):\n            print(z[rows][col],end='|')\n        print('\\n-----------')\n<\/pre>\n\n\n\n
0|1|2|3|\n-----------\n0|1|2|3|\n-----------\n0|1|2|3|\n-----------\n<\/code><\/pre>\n\n\n\n
Functions<\/h5>\n\n\n\n
A piece of code that you only run when we call it is called function<\/strong>. The function can accept parameters that will affect its execution. Let's look at an example:<\/p>\n\n\n\n
def Dokimifunction(onoma,posa=1):\n    timi = onoma+'!'*posa\n    return timi;<\/pre>\n\n\n\n
This function accepts as a parameter a name and as a second parameter a number, which number is the number of times the exclamation mark will appear at the end. In the parameters we can give a default value so that if it has not been declared it will apply:<\/p>\n\n\n\n
*if we didn't do it when we didn't define the number, it would return an error.<\/p>\n\n\n\n
xristis='\u039a\u03ce\u03c3\u03c4\u03b1\u03c2'\nprint(Dokimifunction(xristis))\nprint(Dokimifunction(xristis,5))\n<\/pre>\n\n\n\n
\u039a\u03ce\u03c3\u03c4\u03b1\u03c2!\n\u039a\u03ce\u03c3\u03c4\u03b1\u03c2!!!!!<\/code><\/pre>\n\n\n\n
Error Handling<\/h5>\n\n\n\n
Let's see what the value of the "timi" parameter defined in the function is:<\/p>\n\n\n\n
print(timi)<\/pre>\n\n\n\n
---------------------------------------------------------------------------\nNameError                                 Traceback (most recent call last)\n<ipython-input-226-e0b6617a2c0c> in <module>\n----> 1 print(timi)\n\nNameError: name 'timi' is not defined\n<\/code><\/pre>\n\n\n\n
Oh... the variables inside a function by default are not global, so an opportunity to see how it works error handling<\/strong>:<\/p>\n\n\n\n
try:\n    print(timi)\nexcept:\n    print(\"Oops! \u0394\u03b5\u03bd \u03c5\u03c0\u03ac\u03c1\u03c7\u03b5\u03b9...\")\n\nOops! \u0394\u03b5\u03bd \u03c5\u03c0\u03ac\u03c1\u03c7\u03b5\u03b9...\n<\/code><\/pre>\n\n\n\n
Classes<\/h5>\n\n\n\n
To be able to inherit an object with a set of properties and methods from an initial design we need classes.<\/p>\n\n\n\n
The class consists of one constructor <\/strong>called init<\/strong> and passes its properties to the object being created, a constructor for the parameters called self<\/strong> and from there on we can add other parameters and other functions that it will contain.<\/p>\n\n\n\n
Let's build a quick class that can add and display two numbers:<\/p>\n\n\n\n
class Prosthesi: \n    a = 0\n    b = 0\n    apotelesma = 0\n      \n    #To def __init__ \u03bf\u03bd\u03bf\u03bc\u03ac\u03b6\u03b5\u03c4\u03b1\u03b9 constructor \u03ba\u03b1\u03b9 \u03c7\u03c1\u03b5\u03b9\u03ac\u03b6\u03b5\u03c4\u03b1\u03b9 \u03c0\u03ac\u03bd\u03c4\u03b1 \u03b3\u03b9\u03b1 \u03bd\u03b1 \u03b4\u03b7\u03bc\u03b9\u03bf\u03c5\u03c1\u03b3\u03b7\u03b8\u03b5\u03af \u03c4\u03bf object.\n    #self \u03b5\u03af\u03bd\u03b1\u03b9 \u03bf constructor \u03c4\u03b7\u03c2 \u03b1\u03c1\u03c7\u03b9\u03ba\u03bf\u03c0\u03bf\u03af\u03b7\u03c3\u03b7\u03c2 \u03c4\u03c9\u03bd \u03c0\u03b1\u03c1\u03b1\u03bc\u03ad\u03c4\u03c1\u03c9\u03bd \n    def __init__(self, timi_tou_a, timi_tou_b): \n        self.a = timi_tou_a\n        self.b = timi_tou_b\n      \n    def show(self): \n        print(\"\u03bf \u03c0\u03c1\u03ce\u03c4\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = \" + str(self.a)) \n        print(\"\u03bf \u03b4\u03b5\u03cd\u03c4\u03b5\u03c1\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = \" + str(self.b)) \n        print(\"\u03b7 \u03c0\u03c1\u03cc\u03c3\u03b8\u03b5\u03c3\u03b7 = \" + str(self.apotelesma)) \n  \n    def ipologise(self): \n        self.apotelesma = self.a + self.b\n<\/pre>\n\n\n\n
To make the object with the legacy <\/strong>of the class for the numbers 13 and 28 we execute the following:<\/p>\n\n\n\n
mathimatika=(Prosthesi(13,28))<\/pre>\n\n\n\n
With the name of the function we can call it:<\/p>\n\n\n\n
mathimatika.show()<\/pre>\n\n\n\n
\u03bf \u03c0\u03c1\u03ce\u03c4\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = 13\n\u03bf \u03b4\u03b5\u03cd\u03c4\u03b5\u03c1\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = 28\n\u03b7 \u03c0\u03c1\u03cc\u03c3\u03b8\u03b5\u03c3\u03b7 = 0<\/code><\/pre>\n\n\n\n
We see that the addition returned zero as the function that does the calculation first was not executed. Let's go again:<\/p>\n\n\n\n
mathimatika.ipologise()\nmathimatika.show()<\/pre>\n\n\n\n
\u03bf \u03c0\u03c1\u03ce\u03c4\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = 13\n\u03bf \u03b4\u03b5\u03cd\u03c4\u03b5\u03c1\u03bf\u03c2 \u03b1\u03c1\u03b9\u03b8\u03bc\u03cc\u03c2 = 28\n\u03b7 \u03c0\u03c1\u03cc\u03c3\u03b8\u03b5\u03c3\u03b7 = 41<\/code><\/pre>\n\n\n\n
We see this time it worked fine.<\/p>\n\n\n\n
Modules<\/h5>\n\n\n\n
We can import a package of functions, classes and variables called module with the import command.<\/p>\n\n\n\n
Let's see how we introduce a builtin module for mathematics and call a function to calculate pi:<\/p>\n\n\n\n
import math\nprint(math.pi)<\/pre>\n\n\n\n
3.141592653589793<\/code><\/pre>\n\n\n\n
We can also load only specific functions from the module.<\/p>\n\n\n\n
We can also define an alias for it so that we don't have to call it with the whole name of the module plus the function:<\/p>\n\n\n\n
from random import randrange as rr\n\n#random.randrange(100) \u03b5\u03af\u03bd\u03b1\u03b9 \u03c4\u03bf \u03af\u03b4\u03b9\u03bf \u03bc\u03b5 \u03c4\u03bf \u03b1\u03c0\u03cc \u03ba\u03ac\u03c4\u03c9.\nrr(100)\n<\/pre>\n\n\n\n
How to install a module<\/h5>\n\n\n\n
To install a custom module from the internet the command is pip install<\/strong>:<\/p>\n\n\n\n
pip install pandas<\/pre>\n\n\n\n
I hope you endured until the end, in other articles we will see examples with custom libraries where its real capabilities are hidden.<\/p>\n\n\n\n
Sources:<\/h2>\n\n\n\n
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