Python notes (2)

Continue to List:

Delete elements:

 
a =[1, 2, 3, 4] 
a[2:3] = [] #[1, 2, 4] 
del a[2] #[1, 2] 

To empty the list

 
a[ : ] = [] 
del a[:] 

List is used as a stack (last in, first out) :

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

Use negative index:

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

"+" combination list:

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

Find the number of elements in the list:

 
lst.('hello') # hello  The number of  

Sort the list:

 
sort() 
# Sort the elements of the list appropriately.  

reverse() 
# Invert the elements in the list  

Function pointer problem:

 
def f2(a, L=[]) 
L.append(a) 
return L 

print(f2(1)) # 1 
print(f2(2)) # 1 .  2 L At this function call [1] 
print(f2(3)) # 1 .  2 .  3 

The parameters in the function are:

* parameter name: represents an arbitrary number of parameters

** : represents the dictionary parameter
Control statement:

IF:

 
if x < 0: 
x = 0 
print 'Negative changed to zero' 
elif x == 0: 
print 'Zero' 
elif x == 1: 
print 'Single' 
else: 
print 'More' 

FOR:

 
a = ['cat', 'window', 'defenestrate'] 
for x in a: 
print x, len(x)　　 

WHILE:

 
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: empty action statement

 
while True: 
pass 

Dictionary: data structure for key-value pairs

Use list to construct a dictionary:

 
items = [('name', 'dc'), ('age', 78)] 
d = dict(items) #{'age': 78, 'name': 'dc'} 

Interesting comparison:

 
x = [] #list 
x[2] = 'foo' # error  
x = {} #dictionary 
x[2] = 'foo' # correct  

The content is relatively miscellaneous, learn what write down. Make full use of the spare time and spare time in the work to complete, more fulfilling.