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# Python 3 programming language, learn python, tutorial

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## Python 3. Variables, data types, comments, numbers, text

Reserved words
 And exec Not Assert finally or Break for pass Class from print Continue global raise def if return del import try elif in while else is with except lambda yield
Standard Data Types

• Numbers
• String
• List
• Tuple
• Dictionary
Numbers
• int
• long
• float
• complex
Operations
• - Subtraction
• * Multiplication
• / Division
• % Modulus
• ** Exponent
• // Floor Division
Lets use hello.py file again.

1. Here you can see comments and variable. The variable is vot declared, but interpreter understans it as text:
#  comment
spam = 1  #  comment
#  comment
text = "# This is not a comment"

print (text)

Result:
# This is not a comment

2. Another example:
2 + 2

10 / 10 * 10

2**3 #degree

Result - empty:

There is no error, but there is no result too. Nothing is printed

3. Right example
print( 2 + 2 )

print ( 10 / 10 * 10 )

print ( 2**3 ) #degree

Result:
4
10.0
8

4. Fractions aren't lost when dividing integers. :
print ((50-5*6)/4)
print (8/5)

Result:
5.0
1.6

5. Integer division. It returns the floor:
print (7//3)
print (7//-3)

Result:
2
-3

6. Variables:
x = y = z = 1
print (x)
print (y)
print (z)

Result:
1
1
1

6a. Try:
a, b, c = 1, 2, "john"

print (a)
print (b)
print (c)

7. Unknown variable:
print (zz);

Result:
Traceback (most recent call last):
File "hello.py", line 1, in <module>
print (zz);
NameError: name 'zz' is not defined

8. Complex numbers:
print (1j * 1J)

print (1j * complex(0, 1))

print (3+1j*3)

print ((3+1j)*3)

print ((1+2j)/(1+1j))

a=1.5+0.5j
print (  a.real, a.imag )

print (abs(a)) # SQRT for triangle

Result:
(-1+0j)
(-1+0j)
(3+3j)
(9+3j)
(1.5+0.5j)
1.5 0.5
1.5811388300841898

9. Strings:
a =  'hello python'
print (a)

a = 'doesn\'t hello python'
print (a)

a = "doesn't hello python"
print (a)

a = '"Yes," for python.'
print (a)

a = "\"Yes,\" fort python."
print (a)

a = '"Yes," he said.'
print (a)

a = "\n\
first\n\
second\
third"

print(a)

Result:
hello python
doesn't hello python
doesn't hello python
"Yes," for python.
"Yes," fort python.
"Yes," he said.

first
secondthird

10. You get, what you write. Triple-quotes: """ or ''':
print("""\

Field 1 | Field 2
------------------
1       | 2
3       | 4
------------------
""")

Result:
Field 1 | Field 2
------------------
1       | 2
3       | 4
------------------

11. Show special symbols (r):
a = r"\n\
first\n\
second\
third"

print(a)

Result:
\n\
first\n\
second\
third

11a. Try:
print (r"Hello, \n Python!")

print ("Hello, \n Python!")

12. Text and two variables:
a = 'Help' + 'A'
b = 'Help' + a
print(b)

Result:
HelpHelpA

13. Multiline:
total = "item_one " + \
"item_two " + \
"item_three "

print (total)

14. Strings:
py = 'Hello World!'

print (py)          # Prints complete string

print (py[0])       # Prints first character of the string

print (py[2:5])     # Prints characters starting from 3rd to 5th

print (py[2:])      # Prints string starting from 3rd character

print (py * 2)      # Prints string two times

print (py + "TEST") # Prints concatenated string

15.
S = "Spam"
S  = 'z' + S[1:]
print (S)

Result:
'zpam'

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