# Python notes (2) _python

Source: Internet
Author: User
Continue list:

To delete an element:
Copy Code code as follows:

A =[1, 2, 3, 4]
A[2:3] = [] #[1, 2, 4]
Del a[2] #[1, 2]

Empty list
Copy Code code as follows:

a[:] = []
Del a[:]

List is used as a stack (back-first out):
Copy Code code as follows:

stack = [3, 4, 5]
Stack.append (6)
Stack.append (7)
Stack.pop () # 7
Stack.pop () # 6
Stack.pop () # 5

Index with negative numbers:
Copy Code code as follows:

B=[1, 2, 3, 4]
B[-2] #3

"+" combination list:
Copy Code code as follows:

end = [' st ', ' nd '] + 5*[' th '] + [' XY '] # [' St ', ' nd ', ' th ', ' th ', ' th ', ' th ', ' ', ' ', ' th ', ' xy ']

To find out the number of an element in a list:
Copy Code code as follows:

Lst. (' Hello ') # the number of Hello

List sort:
Copy Code code as follows:

Sort ()
#对链表中的元素进行适当的排序.

Reverse ()
#倒排链表中的元素

Problem with function pointer:
Copy Code code as follows:

def F2 (A, l=[])
L.append (a)
Return L

Print (F2 (1)) # 1
Print (F2 (2)) # 1, 2 L in this function call is [1]
Print (F2 (3)) # 1, 2, 3

The parameters in the function are:

* Parameter name: An argument that represents any number

* *: Indicates dictionary parameter
Control statement:

IF:
Copy Code code as follows:

If x < 0:
x = 0
print ' Negative changed to zero '
elif x = = 0:
print ' Zero '
elif x = = 1:
print ' single '
Else
print ' More '

For:
Copy Code code as follows:

A = [' Cat ', ' window ', ' defenestrate ']
For X in a:
Print x, Len (x)

While:
Copy Code code as follows:

A, b = 0, 1
While B < 1000:
Print B,
A, B = B, a+b
#1 1 2 3 5 8 13 21 34 55 89 144 233 377 610-987

Pass: null Action statement
Copy Code code as follows:

While True:
Pass

Dictionary: Data structure of key-value pairs

Use list to construct dictionary:
Copy Code code as follows:

Items = [(' Name ', ' DC '], (' Age ', 78)]
D = dict (items) #{' age ': +, ' name ': ' DC '}

Interesting comparisons:
Copy Code code as follows:

x = [] #list
X[2] = ' foo ' #出错
x = {} #dictionary
X[2] = ' foo ' #正确

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