In [1]: f = open('foo.txt', 'r') # open a file in read mode
In [2]: print f.read() # Read full content
# Try this in Python shell
import this
In [3]: f = open('foo.txt', 'w') # open a file in write mode
In [4]: f.write('Hello World')
In [5]: f.close()
In [6]: print open('foo.txt', 'r').read()
Hello World
In [7]: f = open('foo.txt', 'a') # open a file in append mode
In [8]: f.write("\nPython is Awesome")
In [9]: f.close()
In [10]: print open('foo.txt', 'r').read()
Hello World
Python is AwesomeIn [1]: open('foo.txt').readlines() # Returns list of lines
Out[1]: ['Hello World\n', 'Python is Awesome']
In [2]: f = open('foo.txt')
In [3]: f.readline() # Returns first line
Out[3]: 'Hello World\n'
In [4]: f.readline() # Returns second line
Out[4]: 'Python is Awesome'
In [5]: f.readline() # Returns third line (absent)
Out[5]: ''
In [6]: f = open('foo.txt', 'a')
In [7]: f.writelines(['\nThird line', '\nFourth line'])
In [8]: f.close()
In [9]: print open('foo.txt', 'r').read()
Hello World
Python is Awesome
Third line
Fourth lineIn [1]: def charcount(filename):
...: return len(open(filename).read())
...:
In [2]: def wordcount(filename):
...: return len(open(filename).read().split())
...:
In [3]: def linecount(filename):
...: return len(open(filename).readlines())
...:
In [4]: charcount('foo.txt')
Out[4]: 52
In [5]: wordcount('foo.txt')
Out[5]: 9
In [6]: linecount('foo.txt')
Out[6]: 4Write a function index(
In [1]: print open('foo.txt').read()
Hello World
Python is Awesome
Third line
Fourth line
In [2]: index('foo.txt')
1. Hello World
2. Python is Awesome
3. Third line
4. Fourth lineIn [1]: def index(filename):
...: lineno = 1
...: with open(filename) as f:
...: for line in f:
...: print("%s. %s" % (lineno, line)),
...: lineno += 1
...:
In [2]: index('foo.txt')
1. Hello World
2. Python is Awesome
3. Third line
4. Fourth lineIn [1]: foo
NameError: name 'foo' is not defined
In [2]: "foo" + 2
TypeError: cannot concatenate 'str' and 'int' objects
In [3]: 2/0
ZeroDivisionError: integer division or modulo by zero
In [4]: open("not-there.txt")
IOError: [Errno 2] No such file or directory: 'not-there.txt'
In [5]: [1, 2, 4][20]
IndexError: list index out of range# catch all exceptions
try:
...
except:
...
# catch just one exception
try:
...
except IOError:
...
# catch one exception, but provide the exception object
try:
...
except IOError, e:
...
# catch more than one exception
try:
...
except (IOError, ValueError), e:
...In [1]: def f1():
...: f2()
In [2]: def f2():
...: try:
...: f3()
...: except Exception as e:
...: print "Exception while executing f3(). Message: %s" % e.message
In [3]: def f3():
...: f4()
In [4]: def f4():
...: raise Exception("Exception occured in f4()")
In [5]: f1()
Exception while executing f3(). Message: Exception occured in f4()In [1]: def factorial(num):
...: import pdb; pdb.set_trace()
...: if num < 0:
...: raise ValueError("Cannot calculate factorial for -ve numbers")
...: elif num in (0, 1):
...: return 1
...: else:
...: return num * factorial(num - 1)
In [2]: factorial(3)
> <ipython-input-1-91b88232d570>(3)factorial()
-> if num < 0:
(Pdb) n
> <ipython-input-1-91b88232d570>(5)factorial()
-> elif num in (0, 1):
(Pdb) n
> <ipython-input-1-91b88232d570>(8)factorial()
-> return num * factorial(num - 1)
(Pdb) c
....
Out[3]: 6#!/usr/bin/env python
f_num = 15 # Global variable: Default number
def factorial(num):
"""
Function to return factorial of a number
"""
if num < 0:
raise ValueError("Cannot calculate factorial for -ve numbers")
elif num in (0, 1):
return 1
else:
return num * factorial(num - 1)
if __name__ == "__main__": # To prevent execution while importing module
print factorial(f_num)