Python2 vs. Python3
Q: Can I install both Python2 and Python3?
A: Yes! I installed both Python3.6 and Python2.7 in my Windows 10.Q: Then how does the system locate and execute of different Python versions?
A: Use Python Launcher for Windows! For command line: type py to launch Python3, and py -2.7 to launch Python2.7, I can also use py -2 to launch the latest version2.x I have installed. Specify version in scripts: #! python: means version2 #! python3: means version3 Also, I can specify a more explicit version: #! python2.7
Q: I have some Python2 scripts, how I can convert them to Python3?
A: Use 2to3.py in ./Toos/scripts folder. For example: $ py C:\Python\Python36-32\Tools\scripts\2to3.py ex1.py A diff against the original source file will be printed. $ py C:\Python\Python36-32\Tools\scripts\2to3.py -w ex1.py -w: Write the modification to a new file, and a backup of the original file is made. $ py C:\Python\Python36-32\Tools\scripts\2to3.py -w -n ex1.py -w -n: Write the modification to a new file, without backup of the original file. $ py C:\Python\Python36-32\Tools\scripts\2to3.py -o ToPython3Project -W -n Python2Project Convert the whole directory 'Python2Project' to python3, save to 'ToPython3Project'. -o: specify the directory to save the output python3 files. -n is required when using -o, because backup files do not make sense when not overwriting the original files. -W: convert the file even if there's no change.Q: What's different between version 2 and version 3?
| Difference | Python2 | Python3 |
|---|---|---|
| print "Hello world!" print "Hello world!", |
print("Hello world!") print ("Hello world!", end(" ")) |
|
| Input | raw_input() | input() |
| Integer division | 1/2, returns 0 | 1/2, returns 0.5 |
| Format | "My name is %s" %"Yifan" |
"My name is {0}".format\('Yifan'\) |
| range() | range() and xrange() | range() behaves like xrange() |
| dict | dict.has_key() | |
| text data | unicode and 8-bit | String and bytes |
Terms:
- PEP : Python Enhancement Proposals
References:
- https://wiki.python.org/moin/Python2orPython3
- https://docs.python.org/3/whatsnew
- Python 3.6.0 documentation