Python 2.4 vs. Python 3.0

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Python 2.4 vs. Python 3.0

One, the print from the statement into a function

Original: Print 1, 2+3

Instead: Print (1, 2+3)

Two, range and xrange

Original: Range (0, 4) result is list [0,1,2,3]

Instead: List (range (0,4))

Original: xrange (0, 4) variable control for the For loop

Instead: Range (0,4)

Three, string

Original: string stored in 8-bit string

Instead: string is stored in 16-bit Unicode string



Iv. changes to the try except statement

Original: Try:

......

Except Exception, E:

......

Switch

Try

......

Except Exception as E:

......

V. Open File

Original: File (...)

or open (...)

Switch

Only open (...)

Six, input a string from the keyboard

Original: Raw_input ("hint message")

Instead: input ("hint message")

Vii.. Bytes data types





A Bytes Object is an immutable array. The items is 8-bit bytes, represented by integers in the range 0 <= x < 256.

Bytes can be thought of as "byte array" objects, each element is a 8-bit byte, and the value range 0~255.

Since strings are stored in Unicode encoding in Python 3.0, when a binary file is written, the string cannot be written directly (or read) and must be encoded in some way into a sequence of bytes before it can be written.

(a) string encoding (encode) is bytes

Example: s = "Zhang San abc12"

b = s.encode (encoded)

# b is the bytes type of data

# Common encoding methods are: "Uft-16", "Utf-8", "GBK", "gb2312", "ASCII", "latin1" and so on.

# Note: An exception is thrown when a string cannot be encoded as a specified "encoding method"

(ii) bytes decoding (decode) as a string

s = "Zhang San abc12"

b = S.encode ("GBK") # string s encoded as a sequence of bytes in GBK format

S1 = B.decode ("GBK") # decodes byte sequence B into a string in GBK format

# description, an exception is thrown when a sequence of bytes cannot be decoded in the specified encoding format

(iii) Examples of using methods

#coding =GBK

f = open ("C:\\1234.txt", "WB")
s = "Dick and Harry Abcd1234"
# -------------------------------
# in python2.4 we can write this:
# F.write (s)
# but throws an exception in Python 3.0
# -------------------------------
b = S.encode ("GBK")
F.write (b)
F.close ()

Input ("?")

An example of reading this file:

#coding =GBK

f = open ("C:\\1234.txt", "RB")
F.seek (0,2) #定位至文件尾
n = F.tell () #读取文件的字节数
F.seek (0,0) #重新定位至文件开始处
b = F.read (n)
# ------------------------------
# in Python 2.4 b is a string type
# to Python 3.0, B is the bytes type
# Therefore, you need to specify the encoding method to confirm the code
# ------------------------------
s = B.decode ("GBK")
Print (s)
# ------------------------------
# in Python 2.4 You can write print s or print (s)
# to Python 3.0 must write print (s)
# ------------------------------
F.close ()
Input ("?")

Should be displayed after running:

Dick and Harry Abcd1234







(iv) bytes sequence, one but formed, whose contents are immutable

Cases:

S= "ABCD"

B=s.encode ("GBK")

Print B[0] # show 65

B[0] = 66

# Execute the sentence, an exception occurred: ' bytes ' object does not the support item assignment





Viii. chr (K) and Ord (c)

Python 2.4.2 before

Chr (k) converts the encoded k to characters, the range of K is 0 ~ 255

Ord (c) takes a single character encoding, the range of return values: 0 ~ 255

Python 3.0

Chr (k) converts the encoded k to characters, the range of K is 0 ~ 65535

Ord (c) takes a single character encoding, the range of return values: 0 ~ 65535

Nine, division operator

Python 2.4.2 before

10/3 Results of 3

Python 3.0

10/3 Results of 3.3333333333333335

10//3 result is 3

Ten, byte array object---New

(i) initialization

A = ByteArray (10)

# A is an array of 10 bytes, each of which is a byte, and the type borrows an int

# at this point, each element has an initial value of 0

(b) The byte array is mutable

A = ByteArray (10)

A[0] = 25

# You can change its elements with an assignment statement, but the assigned value must be between 0 and 255

(c) A slice of a byte array is still an array of bytes

(iv) Converting a string into a byte array

#coding =GBK

s = "Hello"

b = S.encode ("GBK") # first converts a string into bytes by some sort of "GBK" encoding

c = ByteArray (b) #再将 bytes into a byte array

can also write

c = ByteArray ("Hello", "GBK")



(v) byte arrays converted to strings

c = ByteArray (4)

C[0] = 65; c[1]=66; C[2]= 67; C[3]= 68

s = C.decode ("GBK")

Print (s)

# should show: ABCD



(vi) Byte array can be used to write to a text file

#coding =GBK

f = open ("C:\\1234.txt", "WB")
s = "Dick and Harry Abcd1234"
# -------------------------------
# in python2.4 we can write this:
# F.write (s)
# but throws an exception in Python 3.0
# -------------------------------
b = S.encode ("GBK")

F.write (b)
C=bytearray ("Harry", "GBK")
F.write (c)
F.close ()

Input ("?")





Rookiedong's Supplement

1, "Import thread" problem, 2.x module thread in 3.x programming "_thread" (need to be preceded by an underscore). Otherwise, the Importerror:no module named thread will appear.

Python 2.4 vs. Python 3.0