Function
function is a good combination, can be reused, or used to implement the code segment associated with a single function
effect
can be improved and reuse of code modules of an application
to create a function of the
rules of the first function
1. Function block a beginning def keyword followed by the function identifier name and parentheses '()'
2. All incoming parameters and arguments must be enclosed in parentheses, you can define the parameters in parentheses
first statement 3. functions It can be used selectively documentation string, used for function description
4.return [expression] end of the function, a selective return to the caller, return without an expression equivalent to return None
syntax
def function name (parameter list)
function body
call the function
parameter of the function
parameters Category: positional parameters, sequence parameters, keyword parameters, default parameters, keyword arguments dictionary, integrated mass participation
parameter :( formal parameter)
in def-defined function is the function name in brackets behind the variable into the form of parameter
arguments:
providing a variable called actual parameters or when a function call
1. Set transmission parameters
defined:
the actual parameters (arguments) of correspondence between the form of parameters (parameters) corresponding relationship is based on location a corresponding
example:
DEF Student (name, Age, Sex):
Print ( 'name', name )
print ( 'aged', Age)
print ( 'Sex', Sex)
Student ( 'Bob', 15, 'M')
DESCRIPTION:
sequence parameter passing, the sequence of dismantling position parameter correspondence with the
location of the sequence parameter information corresponding to a respective position
2. the sequence parameter passing
sequence parameter passing cycle refers to the function call, with * the parameter passing sequence after transmission manner by dismantling position
3. default parameters passed
when calling a function, if not passed parameters, will use the default parameters
using the default parameters, that is, when defining the function, parameter to a default value if no parameter assignment function to the calling function call will use the default value of this default
Note:
when default parameters when traditional values, the function is called when we pass the implementation of the value of
the default parameter must be placed behind the non-default parameters
parameters 4. keyword
example:
DEF Student (name, Age, Sex):
Print ( 'name', name )
Print ( 'aged', Age)
Print ( 'results', score)
Student ( 'Bob', Age = 15, = 20 is score)
5. The parameter passing keyword dictionary
definition:
Argument refers to the dictionary, the dictionary with '**' dismantling keyword parameter passing after transmission parameters manner
described:
the dictionary of the keys and the parameter name must be the same
dictionary must be a string key name (identifier)
Dictionary of keys to be present in the parameter in
the example:
DEF Student (name, Age, Sex):
Print ( 'name', name)
Print ( 'Age', Age)
Print ( 'achievement', score)
# Student ( ' Bob ', Age = 15, Score = 20 is)
D = {' name ':' Bob ',' Age ': 15,' Score ': 20 is}
Stuident (** D)
integrated parameter passing 6. the function
definition:
function the transmission parameters can be determined in a manner where the parameter can be uniquely matched to the corresponding argument in any combination can
be described:
a position parameter passing (SEQ pass parameters) to the parameter passing the left side of the keyword (keyword dictionary parameter passing) is
def Myfun1 (A, B, C)
Print (A, B, C)
Myfun1 (100, * [200,300])
Myfun1 (* (100,200), 300)
Myfun1 (100, C = 300, B = 200 is)
Myfun1 (100, ** ( 'c ': 300, 'b': 200))
Function to
1. There are no reference function and function parameter
Example:
Summary: variable in function of parameters can replace the contents, the contents can not immutable Alternatively parameter
2. the function returns a value of the function and the return value does not
exercise:
write a function minmax (a, b, c) has three parameters, return these three parameters the minimum and maximum
requirements, forming the tuple , the minimum value of the front, after the maximum
1 def minmax(a,b,c): 2 x=min(a,b,c) 3 y=max(a,b,c) 4 return x,y 5 dl=minmax(50,20,15) 6 print(dl)
1. An asterisk tuple form
syntax:
def function name (* tuple parameter name)
statement block
or
def function name (* args, name keyword parameter)
Role:
Force all parameters must
2. Name the key shape reference
syntax:
def function name (* named key parameter),
a block of statements
or def function name (* args, name keyword parameter):
role:
Force all parameters must pass argument with a keyword or keyword dictionary parameter passing
3. Double asterisks dictionary formed
syntax:
Def function name (parameter name dictionary **)
statement block
effect:
collecting redundant keywords transmission parameters
Description:
dictionary parameter name is usually named 'kwargs'
function of the parameters described
position of the finger parameters, default parameters, the asterisk parameter tuples, double asterisk dictionary parameter can be mixed, the function parameter sequence from left to right are:
a position parameter
asterisk tuple parameter
name keyword parameter
double asterisk shape dictionary ginseng
Variable length parameter function:
asterisk tuples parameter, double asterisk dictionary parameter
Description:
can accept any position mass participation and keywords mass participation
exercise:
write a function similar to the built-in function max mymax
See:
>>> Help (max)
fake mymax max write a function, the function is identical with max
1 def mymax(a,*args): 2 if len(args)==0: #实参个数等于1 3 zhemax=a[0] 4 for x in a: 5 if x>zhemax: 6 zhemax=x 7 return zhemax 8 else: 9 zhemax=a 10 for x in args: 11 if x>zhemax: 12 zhemax=x 13 return zhemax 14 print(mymax([6,8,35,5])) 15 print(mymax(100,200))
Variable Scope
Scope: namespace variables
most basic scope of two variables: the local and global variables
1. The local variables
defined:
1. The definition is called (local parameter is a function of local variables inside a function of variables variable)
2. local variables can only be used within a function
3. local variables can be created when the function is called, after the function call will be automatically destroyed
2. global variables
defined:
the definition of the external, internal function block variable is called global variables
global variables All functions can be accessed directly (single function can not be assigned)
: 3. globals () / locals () function
globals ()
returns the current dictionary global scope variables of
locals ()
dictionary returns the current local scope variables
4. function variable
function name is a variable, a function when it binds def function statement creates
a function may also be passed as an argument another function
function can also be used as a further Returns the value of the number
5. python scope
scopes, also known name space, access the variable is a variable name to find the range space
LEGB
L local scope (the function)
E scope external nested function
G function definitions all modules (toplevel)
B scope of the Python built-in module
6. global statement
1.global statement
action
1, the statement tells the interpreter actuator globa1 statement or more variables, for the scope of these variables scope module level, also referred to as global variables.
2, global declarations (globa1) to map the variable assignment statements inside the module to operate file-scope
grammar
global variable 1, variable 2, ... ...
Description
1. If you want to be assigned global variables inside a function, you must after global declaration (otherwise it will be considered to create a local variable)
2. global variables without declaration inside the function can be accessed directly (variable already exists and is associated with a target)
3. can not declare a local variable, then the global variables declared as global this is not consistent with the provisions of
4. globa1 variable list variable name can not appear in the parameter list for this scope in abnormal operation
abnormal operation
1. error definition and characteristics of
what is wrong: wrong means, etc. Since the logic or grammar leads issue a program can not perform normal
error characteristics: some errors can not predict
2. Exceptional definition
An exception is a program error is a state represented
when an exception occurs, the program will not execute down, and turn to call this function in place pending the error and go back to the normal state
Statement
1.try:
1.try-execpt statement
try:
may trigger the exception in
execpt error type 1 [AS variable 1]
Exception handling statements 1
the except error type 2 [AS Variable 2]:
Exception handling statements 2
the except (error type 3 , error type 4, ... ...) [as variable 3]
exception handling statements 3
the except:
exception handling statements (other)
the else:
no abnormality occurs statement
finally:
final statement
effect of
attempting to acquire abnormal, the abnormal state of the program and perform a normal state to normal
example:
the try - the except statement Description:
variable 1. as a binding errors clause is the object, can be omitted
2. except clause may have one or more, but at least a
3. else clause can only be one and can be omitted
4. finally clause can only be one and can be omitted
5 . else clause of the statement will be executed when the try statement is not an exception occurs
will 6. finally clause statement is executed in any case