Introduction to the python - Letsprogram

Basic concepts in python

Comments in Python start with the hash character, #, and extend to the end of the physical line.

A comment may appear at the start of a line or following whitespace or code, but not within a string literal. A hash character within a string literal is just a hash character. Since comments are to clarify code and are not interpreted by Python, they may be omitted when typing in examples.

# this is the first comment                                             
spam = 1  # and this is the second comment                              
          # ... and now a third!                                        
text = "# This is not a comment because it's inside quotes."            

Let’s try some basic Python commands. Start the interpreter and wait for the python prompt, >>>.

Numbers

The equal sign (=) is used to assign a value to a variable. Afterward, no result is displayed before the next interactive prompt. In Python, we need no to define the variable before using it. But If a variable is not “defined” (assigned a value), trying to use it will give you an error

Using (/) gives you float value of remainder using (//) gives integer value of the remainder.

In addition to int and float, Python supports other types of numbers, such as Decimal and Fraction. Python also has built-in support for complex numbers and uses the j or J suffix to indicate the imaginary part (e.g. 3+5j).

All concepts have an example given below

	>>> 2 + 2
	4
	>>> 50 - 5*6
	20
	>>> (50 - 5*6) / 4
	5.0
	>>> 8 / 5 # division always returns a floating point number
	1.6
	>>> 17 / 3 # classic division returns a float
	5.666666666666667
	>>>
	>>> 17 // 3 # floor division discards the fractional part
	5
	>>> 17 % 3 # the % operator returns the remainder of the division
	2
	>>> 5 * 3 + 2 # result * divisor + remainder
	17
	>>> 5 ** 2 # 5 squared
	25
	>>> 2 ** 7 # 2 to the power of 7
	128
	#..........................................#
	>>> n # try to access an undefined variable
	Traceback (most recent call last):
	File "<stdin>", line 1, in <module>
	NameError: name 'n' is not defined

	#.........................#
	>>> tax = 12.5 / 100
	>>> price = 100.50
	>>> price * tax
	12.5625
	>>> price + _
	113.0625
	>>> round(_, 2)
	113.06
	>>> 4 * 3.75 - 1
	14.0

view raw Introductiontopython.py hosted with ❤ by GitHub

Strings

( \ ) is used to escape quotes in a string.

You can use raw strings by adding an r before the first quote it makes sure to ignore the meaning of ( \n ).

Strings can be concatenated (glued together) with the + operator, and repeated with *

Two or more strings beside each other are concatenated automatically.

All concepts have an example given below

	>>> 'spam eggs' # single quotes
	'spam eggs'
	>>> 'doesn\'t' # use \' to escape the single quote...
	"doesn't"
	>>> "doesn't" # ...or use double quotes instead
	"doesn't"
	>>> '"Yes," they said.'
	'"Yes," they said.'
	>>> "\"Yes,\" they said."
	'"Yes," they said.'
	>>> '"Isn\'t," they said.'
	'"Isn\'t," they said.'
	>>> '"Isn\'t," they said.'
	'"Isn\'t," they said.'
	>>> print('"Isn\'t," they said.')
	"Isn't," they said.
	>>> s = 'First line.\nSecond line.' # \n means newline
	>>> s # without print(), \n is included in the output
	'First line.\nSecond line.'
	>>> print(s) # with print(), \n produces a new line
	First line.
	Second line
	>>> print('C:\sairam\naveen') # here \n means newline!
	C:\sairam
	aveen
	>>> print(r'C:\sairam\naveen') # note the r before the quote
	C:\sairam\naveen
	>>> # 3 times 'un', followed by 'ium'
	>>> 3 * 'un' + 'ium' # strings can be concantenated by using +,*
	'unununium'
	>>> 'Py' 'thon'
	'Python'
	>>> text = ('Put several strings within parentheses '
	... 'to have them joined together.')
	>>> text
	'Put several strings within parentheses to have them joined together.'
	>>> prefix + 'thon'
	'Python'