python-function Instance

1. Definition of Functions

Exercise: Judging if the input is not a number

#!/usr/bin/env pythondef isnum (): Sth = raw_input ("Please input something:") try:if type (int (sth)) = = Type (1):p rint '%s is A number "% sthexcept Exception:print"%s is not a number "% sthisnum ()

2. Parameters of the function

Exercise: Judging if the input is not a number

#!/usr/bin/env Pythonimport sysdef Isnum (s): For I in S:if i in "1234567890":p asselse:print "%s was not a number"% Sbreakel Se:print "%s is a number"% Sisnum (Sys.argv[1])

3. Default parameters for functions

Listdir () function

Exercise: Judging if the input is not a number

#!/usr/bin/env Pythonimport osdef Isnum (s): For I in S:if i in "1234567890":p asselse:breakelse:print SFOR I in (Os.listdir ( "/proc")): Isnum (i)

Note: Default parameters must be written in the back

In [3]: def fun (x=1,y): ...: Print X+yfile "<ipython-input-3-3b7bae6400b0>", line 1def Fun (x=1,y): Syntaxerror:no N-default argument follows default Argumentin [4]: def fun (X,y=1): ...: Print x+y...:in [5]: Fun (2)

4.1 Function variables

Exercise: Functions cannot be assigned to global variables within the function (local), or if they are declared as global variables.

#!/usr/bin/env Pythonx = 1def Fun (): Global Xx+=1print Xfun () print X

Results:

2

2

Exercise 2: Declare the internal variables of the function as global variables, and the external can also be called by the function

#!/usr/bin/env Pythonx = 1def Fun (): global xx + = 1global yy = 3print xprint yfun () print xprint y

Results:

2

3

2

3

Practice 3:locas (): Statistic variable, return dictionary

#!/usr/bin/env Pythonx = 1def Fun (): x = 1y = 1print locals () fun () print locals ()

Results:

{' Y ': 1, ' X ': 1} {' __builtins__ ': <module ' __builtin__ ' (built-in), ' __file__ ': ' 18.py ', ' __package__ ': None, ' x ': 1, ' fun ': <fu Nction fun at 0x7f53bc8938c0>, ' __name__ ': ' __main__ ', ' __doc__ ': None}

5. function return value

Exercise 1: Return none by default

#!/usr/bin/env pythondef Fun ():p rint ' Hello,world ' Print fun ()

Results:

Hello,world

None

Exercise 2: Customize return return value, the statement after return will no longer execute

#!/usr/bin/env pythondef Fun ():p rint "Hello,world" return "Heihei" print "haha" print fun ()

Results:

Hello,world

Heihei

Exercise 3: Determine if the input is a number

Print is seldom used in functions, and return is used to simplify

#!/usr/bin/env Pythonimport osdef Isnum (s): For i in s:if I not in ' 1234567890 ': return Falsereturn truefor i in (os.listdir ("/proc")): If Isnum (i):p rint i

Practice 4:isdigit () to determine if the input is a number

IsDigit (): Determines whether a string is a pure number (script more simplified)

#!/usr/bin/env Pythonimport osdef Isnum (s): If S.isdigit (): Return Truereturn falsefor I in (Os.listdir ("/proc")): If IsNum (i):p rint i

6. Multiple types of values (tuples or dictionaries) and redundant parameters

A tuple only represents one parameter, and a tuple with a *, you can pass the elements in the tuple as parameters to the script; tuples with parameters can only be placed behind, otherwise there is a syntax error

Exercise 1:

In [2]: def fun (x, Y, z): ...: print x + y +z...:in [3]: a = [1,2]in [4]: Fun (3,*a) 6

Error:

In [5]: Fun (*a,3)

File "<ipython-input-5-8a9ea4381ff5>", line 1

Fun (*a,3)

Syntaxerror:only named arguments may follow *expression

Exercise 2:

Dictionary arguments (parameter names and argument names are the same, location doesn't matter)

In [8]: def fun (x, Y, z): ...: print x + y +z...:in [9]: a = {"X": 1, "Y": 2, "z": 3}in [Ten]: Fun (**a) 6

Or:

In [All]: Fun (x=1,y=2,z=3)

6

Exercise 3:

In [1]: def fun (X,*ARGV,**KWARGV): ...: print x.: Print argv ...: print kwargv...:in [2]: Fun (1) 1 ( ){}

Exercise 4:

In the form of an equal sign or dictionary

In [6]: def fun (X,*ARGV,**KWARGV): ...: Print x ...: print argv ...: print kwargv...:in [7]: t = [ ]in [8]: Fun ("A", *t,y=1,**{"B": 1, "C": 2}) 1 (2, ' A ', 1, 2) {' Y ': 1, ' C ': 2, ' B ': 1}

7. Recursive invocation of functions (function call itself)

Conditions:

1) must have the final default result, i.e. if n = = 0

2) Recursive parameters must converge to the default result, i.e. factorial (n-1)

Exercise: factorial, n times f (n-1)

#!/usr/bin/env pythondef factorial (n): if n = = 0:return 1else:return n * factorial (n-1) print factorial (5)

Results:

120

Exercise 2: Accumulation, n plus f (n-1)

#!/usr/bin/env pythondef factorial (n): if n = = 0:return 0else:return n + factorial (n-1) print factorial (5)

Results:

15

python-function Instance