1. Input and Output in python Josh DiCristo

2. How to output numbers str()  You can put any variable holding a number inside the parentheses and it will display the number.  If you put a string inside the parentheses, it returns the original string

3. How to output numbers repr()  Like the str() function, you can put any variable holding a number inside the parentheses and it will display the number.  >>> x = 10 * 3.25  >>> y = 200 * 200  >>> s = 'The value of x is ' + repr(x) + ', and y is ' + repr(y)  >>> print s  The value of x is 32.5, and y is 40000...

4. How to output numbers (cont’d) If a string is put into a repr() command, the resulting string will have quotation marks around it.  >>> s = 'Hello, world.'  >>> print repr(s)  "'Hello, world.'"

5. Differences str() is meant to be readable while repr() is meant to be unambiguous Preciseness  >>> str(1.0/7.0)  '0.142857142857'  >>> repr(1.0/7.0)  '0.14285714285714285'

6. Justifying To align text to the left, use ljust() To align text to the right, use rjust() To align text to the center, use center()  >>> for x in range(1, 11):  print repr(x).rjust(2), repr(x*x).rjust(3), repr(x*x*x).rjust(4) 1 1 1 2 4 8 3 9 27 4 16 64 5 25 125 6 36 216 7 49 343 8 64 512 9 81 729 10 100 1000

7. str.format() Str.format() works like this:  >>> print ‘{} and {}'.format(‘green eggs’, ’ham')  green eggs and ham You can use positional arguments:  >>> print '{1} and {0}'.format('spam', 'eggs')  eggs and spam You can use keyword arguments:  >>> print ‘This {food} tastes {adjective}’.format(food=‘baba ganoush’, adjective=‘divine’)  This baba ganoush tastes divine You can combine them

8. Other commands zfill(n) adds n zeroes to the ends of numbers !r can be used inside brackets to apply repr() to whatever string is going to output in place of the brackets.  >>> print 'The value of PI is approximately {!r}.'.format(math.pi)  The value of PI is approximately 3.141592653589793. The same goes for !s and the str() command

9. Other Commands (cont’d) : can denote how many place an integer is going to be carried out or how much space to put in a column  >>> print 'The value of PI is approximately {0:.3f}.'.format(math.pi)  The value of PI is approximately 3.142.  >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 7678}  >>> for name, phone in table.items():  print '{0:10} ==> {1:10d}'.format(name, phone)  Jack ==> 4098  Dcab ==> 7678  Sjoerd ==> 4127

10. Other Commands (cont’d)  >>> table = {'Sjoerd': 4127, 'Jack': 4098, 'Dcab': 8637678}  >>> print ('Jack: {0[Jack]:d}; Sjoerd: {0[Sjoerd]:d}; 'Dcab: {0[Dcab]:d}'.format(table))  Jack: 4098; Sjoerd: 4127; Dcab: 8637678 You can use ** notation for tables  >>> print 'Jack: {Jack:d}; Sjoerd: {Sjoerd:d}; Dcab: {Dcab:d}'.format(**table) You can use % instead of {} and. instead of :  >>> print 'The value of PI is approximately %5.3f.' % math.pi  The value of PI is approximately 3.142.

11. Opening and Closing files open(filename, mode)  >>> f = open('/tmp/workfile', 'w') mode is optional  w: writes or overwrites onto a new file  a: appends  r: reading (default)  r+: reading and writing  b: Binary mode (windows only) wb, ab, r+b f.close() closes the file

12. File Objects file_object.read() returns the contents of the entire file file_object.readline() returns one line at a time and includes newline characters at the end of the string unless it’s at the end of the file

13. Writing to files file_object.write(‘text’) Only strings may be written to files so any integers must first be converted using str() or repr()

14. Other Commands file_object.seek(offset, from_what)  offset: the integer for how which byte you want to go to  from_what is optional 0: from the beginning of the file (default) 1: from the current position 2: from the end f.seek(4) goes to the 4th character f.seek(-3, 2) goes to the 3rd to last character f.read(1) returns the current character