Python学习笔记(rev.0)
String Manipulation:
Slice indices have useful defaults; an omitted first index defaults to zero, an omitted second index defaults to the size of the string being sliced.
Like strings (and all other built-in sequence type例如 "str"), lists can be indexed and sliced
List Manipulation:
Shallow& Deep Copying:
The difference between shallow and deep copying is only relevant for compound objects (objects that contain other objects, like lists or class instances):
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A shallow copy constructs a new compound object and then (to the extent possible) inserts references into it to the objects found in the original.
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A deep copy constructs a new compound object and then, recursively, inserts copies into it of the objects found in the original.
Demonstration:
import copy
a = [1, 2, 3]
b = [4, 5, 6]
c = [a, b]
#Using normal assignment operatings to copy:
d = c
print id(c) == id(d) # True - d is the same object as c
print id(c[0]) == id(d[0]) # True - d[0] is the same object as c[0]
#Using a shallow copy:
d = copy.copy(c)
print id(c) == id(d) # False - d is now a new object
print id(c[0]) == id(d[0]) # True - d[0] is the same object as c[0]
#Using a deep copy:
d = copy.deepcopy(c)
print id(c) == id(d) # False - d is now a new object
print id(c[0]) == id(d[0]) # False - d[0] is now a new object
