Python at Glance. a really fast (but complete) ride into the Python hole. Paolo Bellagente - ES3 - DII - UniBS

Transcription

1 Python at Glance a really fast (but complete) ride into the Python hole. Paolo Bellagente - ES3 - DII - UniBS

2 Python 2.7 isn t compatible with python 3!!!! Rule #1: RTFM Read The F*****g Funny Manual Rule #2: GIYBF Google Is Your Best Friend

3 Python is interpreted Python has an interactive console

4 Using the console $ python Python (#1, Nov , 13:34:43) [GCC (Red Hat )] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> >>> print "Hello, Python!" Hello, Python!

5 Script Mode Method 1) $ nano test.py print "Hello, Python!" $ python test.py Hello, Python! Method 2) $ nano test.py #!/usr/bin/python print "Hello, Python!" Hello, Python! $ chmod +x test.py # This is to make file executable $./test.py

6 Lines and Indentation if True: print "True" else: print "False" if True: print "Answer" print "True" else: print "Answer" print "False" #!/usr/bin/python import sys try: # open file stream file = open(file_name, "w") except IOError: print "There was an error writing to", file_name sys.exit() print "Enter '", file_finish, print "' When finished" while file_text!= file_finish: file_text = raw_input("enter text: ") if file_text == file_finish: # close the file file.close break file.write(file_text) file.write("\n") file.close()

7 Comments in Python #!/usr/bin/python # First comment print "Hello, Python!" # second comment # This is a comment. # This is a comment, too. # This is a comment, too. # I said that already.

8 Docstrings Autogenerate Doc Formatting with ReStructuredText

9 Assigning Values to Variables #!/usr/bin/python counter = 100 # An integer assignment miles = # A floating point name = "John" # A string print counter print miles print name Simultaneous assignment a = b = c = 1 a, b, c = 1, 2, "john"

10 Python Numbers

11 Python Strings #!/usr/bin/python str = 'Hello World!' print str print str[0] print str[2:5] print str[2:] print str * 2 print str + "TEST" Hello World! H llo llo World! Hello World!Hello World! Hello World!TEST

12 Python Lists #!/usr/bin/python list = [ 'abcd', 786, 2.23, 'john', 70.2 ] tinylist = [123, 'john'] print list # Prints complete list print list[0] # Prints first element of the list print list[1:3] # Prints elements starting from 2nd till 3rd print list[2:] # Prints elements starting from 3rd element print tinylist * 2 # Prints list two times print list + tinylist # Prints concatenated lists

13 #!/usr/bin/python dict = {} dict['one'] = "This is one" dict[2] = "This is two" Python Dictionary tinydict = {'name': 'john','code':6734, 'dept': 'sales'} print dict['one'] This is one print dict[2] This is two print tinydict {'dept': 'sales', 'code': 6734, 'name': 'john'} print tinydict.keys() ['dept', 'code', 'name'] print tinydict.values() ['sales', 6734, 'john']

14 Data Type Conversion More on the tutorials

15 Types of Operator

16 IF #!/usr/bin/python var1 = 100 if var1: print "1 - Got a true expression value" print var1 var2 = 0 if var2: print "2 - Got a true expression value" print var2 print "Good bye!"

17 #!/usr/bin/python ELSE IF var = 100 if var == 200: print "1 - Got a true expression value" print var elif var == 150: print "2 - Got a true expression value" print var elif var == 100: print "3 - Got a true expression value" print var else: print "4 - Got a false expression value" print var print "Good bye!"

18 WHILE LOOP #!/usr/bin/python count = 0 while (count < 9): print 'The count is:', count count = count + 1 print "Good bye!"

19 #!/usr/bin/python FOR for letter in 'Python': # First Example print 'Current Letter :', letter fruits = ['banana', 'apple', 'mango'] for fruit in fruits: # Second Example print 'Current fruit :', fruit print "Good bye!"

20 Switch/Case # define the function blocks def zero(): print "You typed zero.\n" def sqr(): print "n is a perfect square\n" Officially it doesn t exists, it must be replaced by an IF/ELSE series def prime(): print "n is a prime number\n" def even(): print "n is an even number\n" # map the inputs to the function blocks options = {0 : zero, 1 : sqr, 4 : sqr, 9 : sqr, 2 : even, 3 : prime, 5 : prime, 7 : prime, } options[num]()

21 BREAK

22 CONTINUE

23 PASS #!/usr/bin/python for letter in 'Python': if letter == 'h': pass print 'This is pass block' print 'Current Letter :', letter print "Good bye!" Current Letter : P Current Letter : y Current Letter : t This is pass block Current Letter : h Current Letter : o Current Letter : n Good bye!

24 FUNCTION def functionname( parameters ): "function_docstring" function_suite return [expression] def printme( str ): "This prints a passed string into this function" print str return # Now you can call printme function printme("i'm first call to user defined function!") printme("again second call to the same function")

25 PARAMETERS All parameters (arguments) in the Python language are passed by reference. #!/usr/bin/python # Function definition is here def printme( str ): "This prints a passed string into this function" print str return; # Now you can call printme function printme() Traceback (most recent call last): File "test.py", line 11, in <module> printme(); TypeError: printme() takes exactly 1 argument (0 given)

26 Keyword arguments #!/usr/bin/python # Function definition is here def printinfo( name, age ): "This prints a passed info into this function" print "Name: ", name print "Age ", age return; # Now you can call printinfo function printinfo( age=50, name="miki" )

27 #!/usr/bin/python Default arguments # Function definition is here def printinfo( name, age = 35 ): "This prints a passed info into this function" print "Name: ", name print "Age ", age return 0; is it necessary? # Now you can call printinfo function printinfo( age=50, name="miki" ) printinfo( name="miki" )

28 Global vs. Local variables #!/usr/bin/python total = 0; # This is global variable. # Function definition is here def sum( arg1, arg2 ): # Add both the parameters and return them." total = arg1 + arg2; # Here total is local variable. print "Inside the function local total : ", total return total; # Now you can call sum function sum( 10, 20 ); print "Outside the function global total : ", total

29 # content of file support.py def print_func( par ): print "Hello : ", par return Modules #!/usr/bin/python # Import module support import support # Now you can call defined function that module as follows support.print_func("zara")

30 Date & Time class datetime.datetime A combination of a date and a time. Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo. datetime.today() datetime.now([tz]) datetime.utcnow() datetime.fromtimestamp(timestamp[, tz]) datetime.utcfromtimestamp(timestamp) datetime.strptime(date_string, format) %d/%m/%y - %H:%M:%S