February 8, 2018

Introduction to Python

What is Python?

Lightweight scripting programming language

Characteristic

Lightweight, interactive

Download

Official

Installation

Windows environment variable setting (automatic setting selectable)
Confirmation: python in cmd

C:\Users\rakuf\Desktop\wk>python
Python 3.6.4 (v3.6.4:d48eceb, Dec 19 2017, 06:04:45) [MSC v.1900 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.

hello world (interactive mode)

>>> print ("hello world !!!")
hello world !!!

Exit interactive mode

>>> quit ()
C: \ Users \ rakuf \ Desktop \ wk>

Indent

※ Note: You can not recognize without indentation for each block.

Japanese correspondence

code specification required

# test.py
# - * - coding: utf - 8 - * -
# Can use Japanese

variable

# test.py
# - * - coding: utf - 8 - * -
# Definition
a = 1 # number
b = 'ABC' # character string
c = [1, 2, 3, 4, 5] # list
d = {'apple': 10, 'orange': 20, 'banana': 30} # dictionary
# Output
print (a)
print (b)
print (c)
print (d)

result

1
ABC
[1, 2, 3, 4, 5]
{'apple': 10, 'orange': 20, 'banana': 30}

Number

test.py
# - * - coding: utf - 8 - * -
# Definition
a = 1 # int
b = 2.0 # float
c = 3 + 4 j # complex
d = complex (5, 6) # complex
# Output
print (a)
print (b)
print (c.real)
print (d.imag)

result

1
2.0
3.0
6.0
bool
test.py
# - * - coding: utf - 8 - * -
# Definition
a = True # Uppercase is required at the beginning
b = False # First capital required
# Output
print (a)
print (b)

result

True
False

String

# test.py
# - * - coding: utf - 8 - * -
# Definition
# ''
str_1 = 'this is a string.'
# ""
str_2 = "this is a string."
# 'in string
str_3 = 'we can use \' in a string. '
# "in string
str_4 = "we can use \" in a string. "
Edit with # / with newline
str _ 5 = "word 1 \
word 2 "
How to use # r
str_6 = "aaa \ nbbb"
str - 7 = r "aaa \ nbbb"
# Output
print (str - 1)
print (str - 2)
print (str - 3)
print (str - 4)
print (str - 5)
print (str - 6)
print (str - 7)

result

this is a string.
this is a string.
we can use 'in a string.
we can use "in a string.
word 1 word 2
aaa
bbb
aaa\nbbb

String format (%)

# test.py
# - * - coding: utf - 8 - * -
errmsg = "Can not open file"
errcode = 12345
msg = "ERROR:% s (% d)"% (errmsg, errcode)
print (msg)

result

ERROR: Can not open file (12345)

constant

python does not support constants.

Collective type

list

# test.py
# - * - coding: utf - 8 - * -
A 6 ',' A 7 ',' A 8 ',' A 9 '], and A =' 'A 0', 'A 1', 'A 2', 'A 3', 'A 4'
print (a [0])
print (a [3])
print (a [3: 5])
print (a [3:])
print (a [: 5])
for n in a:
     print (n)

result

A0
A3
['A3', 'A4']
['A3', 'A4', 'A5', 'A6', 'A7', 'A8', 'A9']
['A0', 'A1', 'A2', 'A3', 'A4']
A0
A1
A2
A3
A4
A5
A6
A7
A8
A9

tuple

# test.py
# - * - coding: utf - 8 - * -
A 6 ',' A 7 ',' A 8 ',' A 9 '), that is, a = (A 0', A 1 ', A 2', A 3 ', A 4', A 5 '
a [0] = 'A00' # Can not change

result

Traceback (most recent call last):
   File "test.py", line 5, in <module>
     a [0] = 'A00'
TypeError: 'tuple' object does not support item assignment

dictionary

# test.py
# - * - coding: utf - 8 - * -
# Definition
d = {'key 1': 'value 1', 'key 2': 'value 2', 'key 3': 'value 3'}
# Output
print (d ['key 1'])
for k, v in d.items ():
     print (k, v)
for k in d.keys ():
     print (k, d [k])
for v in d.values ():
     print (v)

result

value1
key1 value1
key2 value2
key 3 value 3
key1 value1
key2 value2
key 3 value 3
value1
value2
value 3

Set

# test.py
# - * - coding: utf - 8 - * -
# Definition
a = set (['red', 'yellow', 'blue'])
b = set (['green', 'white'])
# Output, computable
print (a)
print (b)
print (a - b)
print (a | b)
print (a & b)
print (a ^ b)
print ('red' in a)
a.add ('black')
print (a)

result

{'blue', 'yellow', 'red'}
{'white', 'green'}
{'blue', 'yellow', 'red'}
{'blue', 'green', 'yellow', 'red', 'white'}
set ()
{'blue', 'red', 'green', 'yellow', 'white'}
True
{'blue', 'yellow', 'black', 'red'}

Control statement

if else

# test.py
# - * - coding: utf - 8 - * -
a = 10
# if statement Note: indentation match
if a> 10:
     print ('big')
elif a == 10:
     print ('10')
else:
     print ('small')

result

Ten
while
test.py
# - * - coding: utf - 8 - * -
n = 0
# while
While n <5:
     print (n)
     n + = 1
else:
     print ('end')

result

0
1
2
3
Four
end

for, range

# test.py
# - * - coding: utf - 8 - * -
for a in [1, 2, 3]:
     print (a)
print ('---')
for b in {'one': 1, 'two': 2, 'three': 3}:
     print (b)
print ('---')
for c in "123":
     print (c)
print ('---')
# range
for d in range (3): From # 0
     print (d)

result

1
2
3
- -
one
two
three
- -
1
2
3
- -
0
1
2

break

# test.py
# - * - coding: utf - 8 - * -
# break
for n in range (5):
     if n == 3:
         break
     print (n)

result

0
1
2

continue

# test.py
# - * - coding: utf - 8 - * -
# continue
for n in range (5):
     if n == 3:
         continue
     print (n)

result

Exception handling

# test.py
# - * - coding: utf - 8 - * -
# Exceptions
str = '123'
try:
     IndexError occurs because c = str [10] # 10
except IOError:
     print ('IOError')
except IndexError:
     print ('IndexError')
except: # other exceptions
     print ('UnknownError')
else: # if the exception does not occur
     print ('Other')
finally: # Always run
     print ('Finally')

result

IndexError
Finally

function

no return

# test.py
# - * - coding: utf - 8 - * -
# method definition
def printAdd (x, y):
    print (x + y)
Run # method
printAdd (1, 2)

result

return

# test.py
# - * - coding: utf - 8 - * -
# method definition
def add (x, y):
    return x + y
Run # method
print (add (1, 2))

result

default parameter

# test.py
# - * - coding: utf - 8 - * -
# method definition
def repeat_output (msg, n = 3):
    for i in range (n):
        print (msg)
Run # method
repeat_output ('test1',)
print ('-----')
repeat_output ('test2', 5)

result

test1
test1
test1
-----
test2
test2
test2
test2
test2

[*]argument

# test.py
# - * - coding: utf - 8 - * -
# method definition
def method A (x, y, * args):
    print (x)
    print (y)
    print (args)
    print (args [0])
    print (args [1])
Run # method
method A ('x 1', 'y 1', 'Z 1', 'Z 2')

result

x1
y1
('Z1', 'Z2')
Z1
Z2

[**]argument

# test.py
# - * - coding: utf - 8 - * -
# method definition
def method A (x, y, ** args): # also receive dictionary type
    print (x)
    print (y)
    print (args)
    print (args ['k1'])
    print (args ['k2'])
Run # method
args = {'k1': 'v1', 'k2': 'v2'}
method A ('x1', 'y1', ** args) # also receive a dictionary type

result

x1
y1
{'k1': 'v1', 'k2': 'v2'}
v1
v2

Multiple return values

# test.py
# - * - coding: utf - 8 - * -
# method definition
def plusOne (x, y):
    return x + 1, y + 1
Run # method
x, y = plusOne (2, 4)
print (x, y)

result

3 5
Reference to global variable
test.py
# - * - coding: utf - 8 - * -
g = 100
def method_global ():
    print (g)
method_global ()
print (g)

result

100
100

Change global variable failed

# test.py
# - * - coding: utf - 8 - * -
g = 100
def method_global ():
    g = 200 # Overwrite method
    print (g)
method_global ()
print (g)

result

200
100

Successful change of global variable

# test.py
# - * - coding: utf - 8 - * -
g = 100
def method_global ():
    After declaring global g #global, it will be recognized.
    g = 200 # change global variable
    print (g)
method_global ()
print (g)

result

200
200

Class

Definition of class

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class SampleClass:
    "" "this is doc" "" # for doc
    def getName (self):
        return self.name
    def setName (self, name):
        self.name = name
# Create instance
a = SampleClass ()
a.setName ('luohao')
print (a.getName ())

result

luohao

class variable, instance variable

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class SampleClass:
    "" "this is doc" "" # for doc
    count = 0 #class variable
    def __init __ (self): # constructor
        SampleClass.count + = 1
    def getName (self):
        return self.name # instance variable
    def setName (self, name):
        self.name = name # instance variable
# Create instance
a = SampleClass ()
a.setName ('luohao 1')
print (a.getName (), SampleClass.count)
b = SampleClass ()
b.setName ('luohao 2')
print (b.getName (), SampleClass.count)

result

luohao 1 1
luohao 2 2

Access restriction (__)

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class SampleClass:
    "" "this is doc" "" # for doc
    def __init __ (self): # constructor
        self .__ name = 'privateName'
    def __getName (self):
        return self .__ name
# Create instance
a = SampleClass ()
print (a .__ name) # error
print (a .__ getName ()) # error

result

AttributeError: 'SampleClass' object has no attribute '__name'

init and del

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class SampleClass:
    def __init __ (self):
        print ('INIT!')
    def __del __ (self):
        print ('DELETE!')
x = SampleClass ()
del x

result

INIT!
DELETE!

Class inheritance

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class FatherClass:
    def sayFather (self):
        print ('im father')
# Definition of class
class SonClass (FatherClass): Inherit #father class
    def saySon (self):
        print ('im son')
# Create instance
son = SonClass ()
son.sayFather ()
son.saySon ()

result

im father
im son

class inheritance override

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class FatherClass:
    def sayFather (self):
        print ('im father')
# Definition of class
class SonClass (FatherClass): Inherit #father class
    def sayFather (self): #override
        print ('im son')
# Create instance
son = SonClass ()
son.sayFather ()

result

im son

Multiple inheritance of class

# test.py
# - * - coding: utf - 8 - * -
# Definition of class
class FatherClass:
    def sayFather (self):
        print ('im father')
class MotherClass:
    def sayMother (self):
        print ('im mother')
# Definition of class
class SonClass (FatherClass, MotherClass): Inherit #father class
    pass # Do nothing.
# Create instance
son = SonClass ()
son.sayFather ()
son.sayMother ()

result

im father
im mother

Model

# modelTest.py
# - * - coding: utf - 8 - * -
# model
# Definition of class
class ModelClass:
    def printModel (self):
        print ('im from model')

# test.py
# - * - coding: utf - 8 - * -
import modelTest #import
# instance generation from # model
a = modelTest.ModelClass ()
a.printModel ()

result

im from model

Package

# modelTest.py
# - * - coding: utf - 8 - * -
# model
# Definition of class
class ModelClass:
    def printModel (self):
        print ('im from model')

# test.py
# - * - coding: utf - 8 - * -
import modelTest #import
print (__ package__) # package name
print (__ file__) # File name
print (__ name__) # module name

result

None
test.py
__main__

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Introduction to Python

What is Python?

Characteristic

Download

Installation

hello world (interactive mode)

Exit interactive mode

Indent

Japanese correspondence

variable

Number

String

String format (%)

constant

Collective type

list

tuple

dictionary

Set

Control statement

if else

for, range

break

continue

Exception handling

function

no return

return

default parameter

[*]argument

[**]argument

Multiple return values

Change global variable failed

Successful change of global variable

Class

Definition of class

class variable, instance variable

Access restriction (__)

init and del

Class inheritance

class inheritance override

Multiple inheritance of class

Model

Package

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