Python 3.7.x Notes-1 Briefing

Briefing

Easily to learn

1. Efficient high level data structures
2. Simple approach for OO programming
3. Elegant syntax & Dynamic typing

Python interpreter

1. Easily to be extended by C/C++
2. Vast library of source or binary from major Python platform

Using the Python Interpreter

1. Normally install at c:\python37
2. Python command line sample:
   . python -c command [arg]…
   . python -m module [arg]…
3. Argument passing
   . Access the arguments list by import sys.
4. Interactive mode
   . When the command is read from tty, the interpreter will be in interactive mode.
   . In this mode, it promotes the next command with >>>
5. Source code encoding
   . Python source files are treated as UTF-8, so that all most all language char can be stored in string
   . The standard lib is using ASCII

A simple approach to Python

Using Python as calculator

>>> 2 + 2
4
>>> 50 - 5*6
20
>>> (50 - 5*6) / 4
5.0
>>> 8 / 5  # division always returns a floating point number
1.6

>>> 5 ** 2  # 5 squared
25
>>> 2 ** 7  # 2 to the power of 7
128

>>> width = 20
>>> height = 5 * 9
>>> width * height
900

Strings

>>> '"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.

>>> # 3 times 'un', followed by 'ium'
>>> 3 * 'un' + 'ium'
'unununium'

>>> word = 'Python'
>>> word[0]  # character in position 0
'P'
>>> word[5]  # character in position 5
'n'

>>> word[-1]  # last character
'n'
>>> word[-2]  # second-last character
'o'
>>> word[-6]
'P'

 +---+---+---+---+---+---+
 | P | y | t | h | o | n |
 +---+---+---+---+---+---+
 0   1   2   3   4   5   6
-6  -5  -4  -3  -2  -1

List

>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]

>>> squares[0]  # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:]  # slicing returns a new list
[9, 16, 25]

>>> squares + [36, 49, 64, 81, 100]
[1, 4, 9, 16, 25, 36, 49, 64, 81, 100]