2to3.py
2to3 Python program that reads Python 2 source code and applies a series of fixers to transform it into valid Python 3 code.
example1.py file content of Python 2 code at "C:\Python3\" folder:
def greet(name):
print "Hello, {0}!".format(name)
print "What's your name?"
name = raw_input()
greet(name)
C:\Python3> python example1.py
File "example1.py", line 2
print "Hello, {0}!".format(name)
^
SyntaxError: invalid syntax
C:\Python3> python "C:\Python3\Tools\Scripts\2to3.py" -w example1.py
C:\Python3> python example1.py
What's your name?
Linux Mint Mate
Hello, Linux Mint Mate!
A backup of the original Python version 2 file is made and the new file name is called "example1.py.bak".
2to3.py writes the needed modification right back to the source file.
Writing the changes back is enabled with the -w flag.
example1.py file content of Python 3 code:
def greet(name):
print("Hello, {0}!".format(name)) #changed
print("What's your name?") #changed
name = input() #changed
greet(name)
Note
that, this is not a fool-proof conversion though, and you'll likely
need to do some bug-fixing here and there, but it may well be quicker.
Program IDLE Python 3 GUI 64 bit: Shell and File Editor
Start Menu > Python 3 > IDLE (Python 3 GUI - 64 bit)
Python 3 Shell window:
>>> import os
>>> os.getcwd()
'C:\\Python3'
>>>
Python 3 File Editor:
Shell Menu > File > New File Ctrl+N
On the file editor window > press Ctrl+S
Save the file name as time_sleep_eg1.py
Click the Save button
time_sleep_eg1.py file content:
###
import time
repeat = "y"
sentence = []
def sentenceinput():
global sentence, repeat
sentence_length = input("Sentence length: ")
sentence_length = int(sentence_length)
iteration = 0
while iteration < sentence_length:
print("Sentence word ", iteration+1, "? ", sep="", end="")
sentence.append(input())
iteration += 1
print(*sentence)
repeat = input("Repeat? (y/n): ")
print("Let us create one sentence only.")
while True:
time.sleep(1)
if repeat == "y":
sentenceinput()
else:
print("Goodbye!")
break
###
On the file editor window, press F5 to run the module file
Shell output:
###
>>> ================================ RESTART ================================
>>>
Let us create one sentence only.
Sentence length: 3
Sentence word 1? word1
Sentence word 2? word2
Sentence word 3? word3
word1 word2 word3
Repeat? (y/n): y
Sentence length: 2
Sentence word 1? word4
Sentence word 2? word5
word1 word2 word3 word4 word5
Repeat? (y/n): n
Goodbye!
>>>
###
Edit your .py script and press F5 as needed to re-run the script.
Write your Own Function
Code:
def frange(start, stop, step):
i = start
# use floating point inequality check formula
# avoid "while i < stop:"
while (abs(stop-i) > 1e-6):
#print("{0:.1f}".format(i))
yield i
i += step
#frange(0.0, 0.9, 0.1)
for i in frange(0.0, 0.9, 0.1):
#print("{0:.1f}".format(i), end=" ")
print(round(i,1), end=' ')
print() #print new line
Output:
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
Float point inequality test formula:
abs(b - a) > epsilon-error-tolerance
Control structure: while loop
Code:
*listofthings, loops = range(6)
print(listofthings)
print(loops)
loop = 0
while loop < loops:
listofthings[loop] = "thing"+str(loop)
loop += 1
print(listofthings)
Output:
[0, 1, 2, 3, 4]
5
['thing0', 'thing1', 'thing2', 'thing3', 'thing4']
# listofthings is still a list data structure but the list values
modified using array syntax
Function range()
In Python 2 range() produced a list.
In
Python 3, the range() function got its own type. In basic terms, if you
want to use range() in a for loop, then you're good to go. However you
can't use it purely as a list object. For example, you cannot slice a
range type.
sh-4.2# python
Python 2.7.5
>>> range(5)
[0, 1, 2, 3, 4]
>>> type(range(5))
<type 'list'>
>>> exit
Use exit() or Ctrl-D (i.e. EOF) to exit
>>> exit()
sh-4.2#
sh-4.2# python3
Python 3.3.2
>>> range(5)
range(0, 5)
>>> type(range(5))
<class 'range'>
>>> exit()
sh-4.2#
Note that in Python 3, you can still produce a list by passing the generator returned to the list() function as follows:
list1 = list(range(5))
print(list1)
# output is [0, 1, 2, 3, 4]
Human Input syntax
input([prompt])
Python 2 statement uses raw_input to get your input data.
Code:
name = input("What's your OS name? ")
print("My OS name is", name)
Output:
What's your OS name? Linux Mint Mate
My OS name is Linux Mint Mate
Code:
a = input("Enter first number: ")
b = input("Enter second number: ")
a, *numbers, b = range(int(a),int(b)+1,1)
print("The first number is ", a, ",",
"\nthe second number is ", b, " and",
"\nthe numbers between them are ", numbers, ".", sep="")
Output:
Enter first number: 5
Enter second number: 10
The first number is 5,
the second number is 10 and
the numbers between them are [6, 7, 8, 9].
Data Structure Dictionary
Code:
dict1 = { "1":"word1", "2":"word2", "3":"word3" }
for key in dict1:
print(key, ":", dict1[key])
Output:
1 : word1
2 : word2
3 : word3
Data Structure List
list1=["word1", "word2", "word3", "."]
print(list1)
print(len(list1))
print(*list1)
del list1[:]
print(list1)
#Output:
# ['word1', 'word2', 'word3', '.']
# 4
# word1 word2 word3 .
# []
The asterisk allows for each item to be called individually rather than the list.
print syntax
print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)
sep
--- parts separator, by default it is a space, you can change it to any
compatible character that Python allows - this can be used to make the
line shorter or include mathematical operator such as >.
print("Hello, World!")
print("1","2","3", sep="<")
# output is 1<2<3
num = 4
print("The number num is ", num, " or 2*2=", 2*2, sep="")
# output is:
# python3 main.py
# The number num is 4 or 2*2=4
end
--- end of the line, to leave a space rather than starting a new line,
you can use print(x, end=' '). By default, it creates a line break.
print("line1","line1;",end=" ")
print("line1 also")
# output is line1 line1; line1 also
file=sys.stdout --- you construct the string as you would normally to print out anything and then append the file option
From Python 2 code:
print >>sys.stderr, "an error"
print "no error"
To Python 3 code:
import sys
print("an error", file=sys.stderr)
print("fatal error", file=sys.stderr)
print("no error")
flush --- if True will force the print stream to flush after execution
Python Comment Symbol
Python comment symbol is #
# single line comment
Python Abbreviations
PEP --- Python Enhancement Proposal
PSF
--- The Python Software Foundation is an organization devoted to
advancing open source technology related to the Python programming
language
PyPI --- Python Package Index
Python 3 Information
Python 3 was to make changes to the language primarily to remove the warts that had grown in the preceding versions.
Python 3 was not to be a complete redesign(revolution), but instead an evolution of the language.
Maintaining
"full" backward compatibility, unnecessary syntax, unnecessary semantic
acceptable with Python 2 were explicitly off-the-table.
Python 2
code can be translated fairly easily to Python 3, sometimes entirely
mechanically by such tools as 2to3. There is also non-trivial subset of
the language that will run without modification on both versions 2 and
3.
The end of life for Python 2.7 has been announced.
Python 2.7 itself is the last version of the Python 2.x line with firm plans to not release a Python 2.8.
Python 2.7 will stop receiving bug fixes and other updates in 2020.
Get your code ported over to Python 3.
Python
4 that is not going to happen any time soon so you should be fine to
safely port to version 3 without worrying about a massive jump in the
future.
Internet Resources
Download Python 3
https://www.python.org/downloads/
Stack
Overflow, this website operates on a reward system for correct answers,
so people are always willing to pitch in and help out others
