Python:the difference between append and extend

Data Analysis:indoor localization using received signal strength (RSS)

An error about the list operation in Python:append and extend elements

We define a list A to storage objects, which the length was unknown, and list B and C to storage the final result.

The code like bellow:

# BEGIN

A = []

B = []

C = []

For obj in range (110):

Add ten objects to a, a = [a0,a1,a2....a9]

B.extend (A)

C.append (A)

Del a[:]

# End

The expected result is:

B = [A0, a1, A2,a3 ..., a 1098, a1099]//which has 1100 elements

C = [[A0, A1....a9], [A10, A11...a19] .... [a1090, a1091...a1099]] which has elements

But when I run the code, the bug appear, the real result as follow:

B = [A0, a1, A2,a3 ..., a 1098, a1099]//which has 1100 elements

C = [[], [] .... []]//which have nothing in each list

Then I the difference between append and extend through Google

Append:append object to the end

Extend:extend List by iterable

Finally, I Print the result in each cycle, the list B using extend looked fine, but the list C using append came wrong, it showed like bellow:

C = [[A1]]

C = [[A2],[A2]]

C = [[A3],[a3],[a3]]

.....

C = [[a109],[a109],... [A109]]

Then I make a deep copy from A to D and then append the D to the C and like bellow:

# BEGIN

A = []

B = []

C = []

For obj in range (110):

Add ten objects to a, a = [a0,a1,a2....a9]

B.extend (A)

D = Copy.deepcopy (A)

C.append (D)

Del a[:]

# End

Run the code and the result came right.

So, when using extend, it'll copy all elements in A to the list B, and when using append, it'll only copy the address of a to list C, so, in the end, the A would be empty, which caused the result:list C have nothing.

Python:the difference between append and extend