"Basic Python Tutorial" reading notes the sixth chapter abstract function parameters

6.1 Creating a function

A function can be called (possibly containing a parameter, that is, a value placed in parentheses), which performs some behavior and returns a value. In general, the built-in callable function can be used to determine whether a function can be called:

>>> x=1

>>> y=math.sqrt

>>> Callable (x)

False

>>> Callable (Y)

True

Define a function with a def statement:

def fib (num):
result=[0,1]
for I in range (num-2):
Result.append (Result[-2]+result[-1])
return Result

6.1.1 Record function

To add a document string to a function:

>>> def Square (x):

' Calculates the square of the number X '

Return x*x

The document string can be visited as follows:

>>> square.__doc__

' Calculates the square of the number X '

By using help in the interactive interpreter, you can get information about the function, including its document string:

>>> Help (Square)

Help on Function Square:

Square (x)

Calculates thesquare of the number X

6.2.1 Parameters

Assigning a new value to a parameter within a function does not change the value of any external variable:

>>> def try_to_change (n):

N= ' Mr.gumby '

>>> name= ' mrs.entity '

>>> Try_to_change (name)

>>> Name

' Mrs.entity '

Default value of the parameter:

>>> def hello (greeting= ' hello ', name= ' world '):

print '%s,%s! '% ( Greeting,name)

>>> Hello ()

hello,world!

>>> hello (' greeting ')

greeting,world!

>>> hello (' greeting ', ' universe ')

greeting,universe!

6.2.2 Collect parameters:

The asterisk before the parameter places all values in the same tuple.

>>> def print_params (*params):

Print params

>>> print_params (' testing ')

(' testing ',)

>>> (Print_params)

(1, 2, 3)

Joint Common parameters

>>> defprint_params_2 (title,*params):

Print title

Print params

>>>print_params_2 (' params: ')

Params:

(1, 2, 3)

If no element is provided for collection, the params is an empty ancestor

>>> print_params_2 (' Nothing: ')

Nothing

()

Cannot handle keyword parameters:

>>>print_params_2 (' Hmm ... ', something=42)

Traceback (most recent):

File "<input>", line 1, in <module>

Typeerror:print_params_2 () got anunexpected keyword argument ' something '

Can handle the "collect" operation of the keyword parameter:

>>> def Print_params_3 (**params):

.. print params

...

>>> Print_params_3 (x=1,y=2,z=3)

{' Y ': 2, ' X ': 1, ' Z ': 3} #返回的是字典而不是元组

Put together with:

>>> Defprint_params_4 (X,y,z=3,*pospar,**keypar):

... print x, Y, Z

... print Pospar

... print Keypar

...

>>>print_params_4 (1,2,3,5,6,7,foo=1,bar=2)

1 2 3

(5, 6, 7)

{' Foo ': 1, ' Bar ': 2}

>>> (Print_params_4)

1 2 3

()

{}

Implement multiple names to store at the same time:

>>> def init (data):

data[' first ']={}

data[' Middle ']={}

data[' last ']={}

Def lookup (Data,label,name):

return Data[label].get (name)

def store (data,*full_names):

For Full_name in Full_names:

Names=full_name.split ()

If Len (names) ==2:names.insert (1, ")

Labels= ' first ', ' Middle ', ' last '

For label,name in Zip (labels,names):

People=lookup (Data,label,name)

If people:

People.append (Full_name)

Else

Data[label][name]=[full_name]

>>> Store (d, ' Luke Skywalker ', ' Anakin Skywalker ')

>>> lookup (d, ' last ', ' Skywalker ')

[' Luke Skywalker ', ' anak in Skywalker ']

6.2.3 reversal Process

>>> def add (x, y): Return x+y

>>> (params=)

>>> Add (*params)

3

Working with Dictionaries:

>>> defhello_3 (greeting= ' Hello ', name= ' world '):

... print '%s,%s! '% ( Greeting,name)

...

>>> params={' name ': ' Sirrobin ', ' greeting ': ' Well met '}

>>> Hello_3 (**params)

Well Met,sir robin!

Asterisks are only useful when defining functions (allowing the use of an indefinite number of arguments) or calling ("splitting" a dictionary or sequence).

6.3 Scopes

Outside the global scope, each function call creates a new scope:

>>> def foo ():

... x=42

...

>>> x=1

>>> foo ()

>>> x

1

The assignment statement x=42 only works in the internal scope (local namespace), so it does not affect the X in the outer (global) scope. Variables within a function are called local variables (the local variable, which is the opposite of global variables). Parameters work like local variables, so it is not a problem to use the name of the global variable as the parameter name.

To access global variables inside a function:

>>> def combine (parameter):p rintparameter+external

>>> external= ' Berry '

>>> combine (' shrub ')

Shrubberry

6.4 Recursion

A useful recursive function consists of the following parts:

When a function returns a value directly, there is a basic instance (least possible problem), a recursive instance, including one or more recursive invocations of the smallest number of problems.

6.4.12 Classics: Factorial and Power

>>> def factorial (n):

... result=n

... for I in range (1,n):

... result*=i

... return result

...

>>> factorial (5)

120

Or:

>>> def factorial (n):

... if n==1:

... return 1

.. else:

... return n*factorial (n-1)

...

>>> factorial (5)

120

Power of calculation:

>>> def Power (x,n):

... result=1

... for i in range (n):

... result*=x

... return result

...

>>> Power (2,3)

8

Or:

>>> def Power (x,n):

... if n==0:

... return 1

.. else:

... return x*power (x,n-1)

...

>>> Power (2,3)

8

New functions in this chapter:

Map (func,seq[,seq,...]) : Apply a function to each element in a sequence

Filter (func. Seq): Returns the list of elements whose function is true

Reduce (func,seq[,initial]): Equivalent to Func (func (seq[0],seq[1]),...)

SUM (SEQ): Returns all the elements in the SEQ and

Apply (Func[,args[,kwargs]]): Call function, can provide parameters

"Basic Python Tutorial" reading notes the sixth chapter abstract function parameters