Detailed explanation of how to represent matrices in Python

This article mainly introduces the method of expressing matrices in Python, and analyzes the methods of expressing matrices in Python and related operations based on specific examples. Notes, friends in need can refer to the following

The examples in this article describe the method of representing matrices in Python. Share it with everyone for your reference, the details are as follows:

In c language, it represents an "integer 3 rows and 4 columns" matrix, which can be declared like this: int a[3][ 4]; In python, variables int cannot be declared, and dimensions cannot be listed. It can be expressed in the form of a list within a list. For example:

represents matrix , it can be like this:

count = 1
a = []
for i in range(0, 3):
  tmp = []
  for j in range(0, 3):
    tmp.append(count)
    count += 1
  a.append(tmp)
print a

Result:

[[1, 2, 3], [4, 5, 6], [7, 8, 9]]

But pay attention to one thing: initialization (when all assignments are 0), the following is wrong ! !

tmp = []
for j in range(0, 3):
  tmp.append(0)
a = []
for i in range(0, 3):
  a.append(tmp)
print a

Result:

[[0, 0, 0], [0, 0, 0], [0, 0, 0]]

Cause: The tmp of such a list is the same. If you change any row, other rows will be changed accordingly. Be careful! ! , the following is correct:

a = []
for i in range(0, 3):
  tmp = []
  for j in range(0, 3):
    tmp.append(0)
  a.append(tmp)
print a

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