Python Learning Notes (statement)

For more information on print and import, use the comma output

>>> print ' Age: ', 42
Age:42

>>>
(1, 2, 3)
>>> Print
1 2 3
>>> print (+/-)
(1, 2, 3)

>>> name= ' Gumby '
>>> salutation= ' Mr. '
>>> greeting= ' Hello, '

>>> print greeting, salutation, name
Hello, Mr Gumby.

print ' Hello, ',
print ' world! '

------------------

Hello, world!.

To import something as another thing

When importing functions from a module, you can use the

Import Somemodule

Or

From Somemodule import somefunction

Or

Form Somemodule Import Somefunction.anotherfunction.yetanotherfunction

Or

Form Somemodule Import *

Two modules have the same function, you can use an alias

>>> import Math as foobar# to provide aliases for modules
>>> Foobar.sqrt (4)
2.0
>>> from math import sqrt as Foobar #为函数提供别名
>>> Foobar (4)
2.0
>>> from Module1 import open as Open1

>>> from module2 import open as Open2

Assignment Magic Sequence Unpacking

>>> x,y,z=1,2,3
>>> print x, Y, Z
1 2 3
>>> x,y=y,x
>>> print x, Y, Z
2 1 3

>>> values=1,2,3
>>> values
(1, 2, 3)
>>> x,y,z=values
>>> x
1
>>> scoundre={' name ': ' Robin ', ' girlfriend ': ' Marion '}
>>> Key,value=scoundre.popitem ()
>>> Key
' Girlfriend '
>>> value
' Marion '
>>>

Chained assignment

X=y=somefunction ()

Equivalent to

X=somefunction ()

Y=x

Increment assignment

>>> x=2
>>> x+=1
>>> x*=2
>>> x
6
>>> fnord= ' foo '
>>> fnord+= ' Bar '
>>> fnord*=2
>>> Fnord
' Foobarfoobar '
>>>

Conditional statements

False None 0 "" () [] {} is false and the rest is interpreted as true

>>> True
True
>>> False
False
>>> true==1
True
>>> false==0
True
>>> true+false+42
43

>>> BOOL (' I think, therefore I am ')
True
>>> BOOL (42)
True
>>> bool (')
False
>>> BOOL (0)
False

If statement

Name=raw_input (' What's your name? ')
If Name.endswith (' Gumby '):
print ' Hello,mr.gumby '

ELSE clause

Name=raw_input (' What's your name? ')
If Name.endswith (' Gumby '):
print ' Hello,mr.gumby '
Else
print ' Hello,stranger '

elif clause

Num=input (' Enter a number: ')
If num>0:
print ' The number is positive '
Elif num<0:
print ' The number is negative '
Else
print ' The number is zero '

Nested code blocks

Name=raw_input (' What's your name? ')
If Name.endswith (' Gumby '):
If Name.startswith (' Mr. '):
print ' Hello,mr.gumby '
Elif name.startswith (' Mrs. '):
print ' Hello,mrs.gumby '
Else
print ' Hello,gumby '
Else
print ' Hello,stranger '

Assertion

Use keyword assert in statement

>>> age=10
>>> assert 0<age<100
>>> Age=-1
>>> assert 0<age<100

Traceback (most recent):
File "<pyshell#3>", line 1, in <module>
Assert 0<age<100
Assertionerror
>>> Age=-1
>>> assert 0 <age<100, ' The must be realistic '

Traceback (most recent):
File "<pyshell#5>", line 1, in <module>
Assert 0 <age<100, ' The must be realistic '
Assertionerror:the must be realistic

Loop while loop

X=1
While x<=100:
Print X
X+=1

Name= "
While not name:
Name=raw_input (' Please enter your name: ')
print ' hello,%s! ' %name

For

words=[' This ', ' was ', ' an ', ' ex ', ' Parrot ']
For word in words:
Print Word

numbers=[0,1,2,3,4,5,6,7,8,9]
For number in numbers:
Print number

Range (10)

-----------------------

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

For number in range (1,101): #包含下限, with no upper bound
Print number

-----------------------

1

2

.

.

100

Range and Xrange

>>> A=range (0,100)
>>> print Type (a)
<type ' list ' >
>>> Print a
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60 3, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
>>> Print A[0],a[1]
0 1
>>> A=xrange (0,100)
>>> print Type (a)
<type ' xrange ' >
>>> Print a
Xrange (100)
>>> Print A[0],a[1]
0 1
>>>

Traverse Dictionary

d={' x ': 1, ' Y ': 2, ' Z ': 3}
For key in D:
Print key, ' corresponds to ', D[key]

---------------------

>>>
Y corresponds to 2
x corresponds to 1
Z corresponds to 3

d={' x ': 1, ' Y ': 2, ' Z ': 3}
For Key,value in D.items ():
Print key, ' corresponds to ', value

--------------------------------

Y corresponds to 2
x corresponds to 1
Z corresponds to 3

Some iterative tools parallel iterations

names=[' Anne ', ' Beth ', ' George ', ' Damon '
AGES=[12,45,32,102]
For I in range (len (names)):
Print Names[i], ' is ', ages[i], ' years '

----------------------------

>>>
Anne is-years old
Beth is years old
George is years
Damon is 102 years old
>>>

The ZIP function is used for parallel iterations

>>> names=[' Anne ', ' Beth ', ' George ', ' Damon '
>>> ages=[12,45,32,102]
>>> Zip (names,ages)
[(' Anne ', '), (' Beth ', '), (' George ', ' + '), (' Damon ', 102)]

>>> for name,age in Zip (names,ages):
Print name, ' is ', age, ' years '

Anne is-years old
Beth is years old
George is years
Damon is 102 years old
>>> Zip (Range (5), xrange (10000000))
[(0, 0), (1, 1), (2, 2), (3, 3), (4, 4)]
>>>

Numbering iterations

>>> index=0
>>> for string in strings:
If ' xxx ' in string:
strings[index]=[' censored ']
Index+=1

Using the built-in function enumerate

>>> for index,string in Enumerate (strings):
If ' xxx ' in string:
strings[index]=[' censored ']

Flip and sort iterations

>>> sorted ([4,3,5,8,6])
[3, 4, 5, 6, 8]
>>> sorted (' hello,world! ')
['! ', ', ', ' d ', ' e ', ' h ', ' l ', ' l ', ' l ', ' o ', ' o ', ' R ', ' W ']
>>> list (Reversed (' hello,world! '))
['! ', ' d ', ' l ', ' r ', ' O ', ' w ', ', ', ' o ', ' l ', ' l ', ' e ', ' H ']
>>> ". Join (Reversed (' hello,world! '))
'!dlrow,olleh '
>>>

Jump out of Loop break

>>> from math import sqrt
>>> for N in range (99,0,-1):
ROOT=SQRT (N)
If Root==int (root):
Print n
Break

81
>>>

Continue

For x in SEQ:
If Condition1:continue
If Condition2:continue
If Condition3:continue

Do_someting ()

Do_someting_else ()

Do_another_thing ()

ECT ()

While True/break

>>> word= ' Dummy '
>>> while Word:
Word=raw_input (' Please enter a world: ')
print ' The word was ' +word

Please enter a World:first
The word was first
Please enter a World:sencond
The word was Sencond
Please enter a World:third
The word was third
Please enter a world:dummy
The word was dummy
Please enter a world:
The word was
>>>
>>> while True:
Word=raw_input (' Please enter a word: ')
If not word:break
print ' The word was ' + word

Please enter a word:d
The word wasd
Please enter a word:
>>>

Else clause in a loop

>>> from math import sqrt
>>> for N in range (99,81,-1):
ROOT=SQRT (N)
If Root==int (root):
Print n
Break
Else
print "didn ' t find it!"

Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
Didn ' t find it!
>>>

List derivation--lightweight loops

>>> [x*x for X in range (10)]
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
>>> [x*x for x in range (ten) if x%3==0]
[0, 9, 36, 81]

>>> [(x, Y) for x in range (3) for Y in range (3)]
[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1)]
>>> result=[]
>>> for x in range (3):
For y in range (3):
Result.append ((x, y))

>>> List (Result)
[(0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (2, 1)]
>>>

Pass

If name== ' Ralph Auldus melish ':
print ' welcome! '
Elif name== ' Enid ':
Pass
Elif name== ' Bill Gates ':
print ' Access Denied '

Del

>>> x=[' hello ', ' world '
>>> y=x
>>> y[1]= ' Pyhton '
>>> x
[' Hello ', ' Pyhton ']
>>> del X
>>> y
[' Hello ', ' Pyhton ']

Python Learning Notes (statement)