First, a list of derivation of formula
Even-numbered less than 10
li = [0,2,4,6,8,10] li = list (range (0,11,2))
And repeated with
li=[]
for i in range(0,11,2):
li.append(i)
print(li)
List can also be used to derive the formula
Original formula:
Li = []
for I in Range (21 is):
IF I% 2 == 0:
li.append (I)
is equivalent to:
LI2 = [I for I in Range (21 is)% 2 == 0 I IF ] i # a first element that corresponds to the the append
LI3 = [ 'a' for i in Range (21 is) IF i% 2 == 0] # if you are an even number, in a list of Riga 'a'
LI4 = [i if i% 2 == 0 else 'a' for i in range (21)] # satisfied if the even add a i, otherwise add an 'a'. to add more conditions must be put back for
Second, the iterative and generator
1, iterators
Iterator object requires support for the iterator protocol objects in Python, support the iterator protocol is to achieve the object __iter __ () and __next __ () method.
Wherein the __iter __ () method returns an iterator object itself; __ __ Next () returns the next container element method, initiated at the end of the StopIteration exception.
li = [1,2,3] # only iter, there is no next, it is not an iterator
li [1] # Returns the index of the element 1, 2
li .__ ITER __ () # li returns the iterator itself (the change li into an iterator), there is a trim function iter acting as
g = li .__ iter __ () # assignment
built-in functions: Next ()
Next (G) # returns the index 0, to achieve the role of the iterator, with g .__ nest__ () acts like
next (g) # returns the index value of 0
next (g) # returns the index value of 0
next (g) # error StopIteration
NOTE: You must assign a value () after the iter to a variable, otherwise it will redefine
cycle:
G = ITER (Li)
for I in G:
Print (I, End = '')
output: 1 2 3
2, generator generator
Fun DEF ():
I =. 1
the while I <. 5:
Print (I)
the yield 'STOP' # plus side put fun () into an iterator, the call next () is to play the role of blocker (pause), plus (similar to the return on the role, will output 'stop') 'stop'. Total character on it, is to achieve a builder functions: pause, return value
I + =. 1
Print ( 'AAA', I)
Next () # output. 1
Next () # output AAA 2
2
Next () # Output: aaa 3
3
generator is essentially an iterator
Feibolaqi number
1,1,2,3,5,8,13,21,34 ,. . .
A number generator to write Feibolaqi
DEF FIB (NUM):
n-# = 0 indicates generations
A, B = 0,1
the while n-<NUM:
Print (B) represents the amount that #b to generation
if n% 10 0 ==:
the yield # add a generator can see a
a, B = B, a + B
n-+. 1 =
Third, the package module, and
Module: py file
Package: Many py files in a folder
Methods: Functions
Properties: variable name
1, built-in module
2, third-party modules
3, the import module
import copy # import entire module from copy import deepcopy # turned large modules inside the small module, saving memory, designated introduced
May also be introduced to cmd.exe pip
4, a custom module
The same path: direct import file name
Different paths: With one other module sys sys.path will find from your python installation path
import sys # function call sys sys.path # search for your python folder all py file path sys.path.append (r 'absolute path') # absolute path to your import import absolute path where the module can then # the calling module
__main__ meaning:
When the file is run directly is, __name__ document is __main__, when the file is imported, __ name__ is the file name