Chapter 18: The C++ I/O System

Example 18.1, Page Number: 421

In [1]:
class three_d:
    def __init__(self,a,b,c):   #3D coordinates
        self.x=a
        self.y=b
        self.z=c
    #Display x,y,z coordinates - three_d inserter.
    def __repr__(self):
        return str(self.x)+", "+str(self.y)+", "+str(self.z)+"\n"

#Variable declaration
a=three_d(1,2,3)
b=three_d(3,4,5)
c=three_d(5,6,7)

#Result
print a,b,c

1, 2, 3
 3, 4, 5
 5, 6, 7

Example 18.2, Page Number: 423

In [2]:
class thrnee_d:
    def __init__(self,a,b,c):   #3D coordinates
        self.x=a
        self.y=b
        self.z=c
    #Display x,y,z coordinates - three_d inserter.
    __repr__=repr                              
       
#Friend function        
def repr():
    return str(self.x)+", "+str(self.y)+", "+str(self.z)+"\n"

#Variable declaration
a=three_d(1,2,3)
b=three_d(3,4,5)
c=three_d(5,6,7)

print a,b,c

1, 2, 3
 3, 4, 5
 5, 6, 7

Example 18.3, Page Number: 424

In [3]:
class three_d:
    def __init__(self,a,b,c):   #3D coordinates
        self.x=a
        self.y=b
        self.z=c
    #Display x,y,z coordinates - three_d inserter.
    def __repr__(self):
        return str(self.x)+", "+str(self.y)+", "+str(self.z)

#Variable declaration
a=three_d(1,2,3)

print a

#User input
print "Enter X,Y,Z values:"
a=three_d(4,5,6)   
print a

1, 2, 3
Enter X,Y,Z values:
4, 5, 6

Example 18.4, Page Number: 428

In [4]:
print '{0:+d}'.format(123),   #for ios::showpos
if(123.23>0):
    i='{0:e}'.format(123.23)  #for ios::scientific  
    i='+'+i
    print i
else :
    print '{0:e}'.format(123.23)
   

+123 +1.232300e+02

Example 18.5, Page Number: 430

In [1]:
import string

print '{0:+d}'.format(123),        #for ios::showpos
if(123.23>0):
    i='{0:e}'.format(123.23)       #for ios::scientific  
    i='+'+i
    print i
else :
    print '{0:e}'.format(123.23)

    
print '{:10.2f}'.format(123.23),   #2 digits left of decimal
if(123.23>0):
    i='{0:.2e}'.format(123.23)     #for ios::scientific  
    i='+'+i
    print i
else :
    print '{0:.2e}'.format(123.23)
    
    
print '{:#>10}'.format(str(123)),  #for ios::fill
if(123.23>0):                      
    i='{0:.2e}'.format(123.23)  #for ios::scientific  
    i='+'+i
    print i
else :
    print '{0:.2e}'.format(123.23)

+123 +1.232300e+02
    123.23 +1.23e+02
#######123 +1.23e+02

Example 18.6, Page Number: 432

In [5]:
print '{0:.0e}'.format(1000.243)        #for setprecision
print '{:>20}'.format("Hello There")    #to set width and right align

1e+03
         Hello There

Example 18.7, Page Number: 433

In [6]:
print '{0:+d}'.format(123),   #for ios::showpos
if(123.23>0):
    i='{0:e}'.format(123.23)  #for ios::scientific  
    i='+'+i
    print i
else :
    print '{0:e}'.format(123.23)
   

+123 +1.232300e+02

Example 18.8, Page Number: 433

In [7]:
#User input
s="   Hello"

#Result
print s.lstrip()    #lstrip removes leading spaces

Hello

Example 18.9, Page Number: 434

In [2]:
def setup(s):
    return '{:$<10}'.format(str(s))


#Result
print 10,setup(10)

10 10$$$$$$$$

Example 18.10, Page Number: 435

In [ ]:
def prompt():
    print "Enter number using hex format:"
    hex=0x46
    return hex


#Result
i=prompt()
print i

Example 18.11, Page Number: 438

In [8]:
 
out=open("test",'w')


if(not(out)):
    print "Cannot open file."
else:
    #Write to file
    out.write("10 123.23\n")
    out.write("This is a short text file.")
    #Close the file
    out.close()

Example 18.12, Page Number: 438

In [9]:
 
In=open("test",'r')
 
if(not(In)):
    print "Cannot open file."
else:
    #Read file
    i=In.read(2)
    ch=In.read(1)
    f=In.read(6)
    str=In.read()
    print i,f,ch
    print str
    #Close the file
    out.close()

10 123.23  

This is a short text file.

Example 18.13, Page Number: 439

In [10]:
import sys
                                     
if not(len(sys.argv)==2):
    print "Usage: PR <filename>\n"
else:
    #Open a file
    In=open(sys.argv[1],'r')

    #In case file cannot open
    if(not(In)):
        print "Cannot open file."
    else:
        #Read file
        ch=In.read()
        print ch
        In.close()
    

Usage: PR <filename>

Example 18.14, Page Number: 440

In [11]:
import sys

p="hello there"

out=open("test",'w')

#In case file cannot open
if(not(out)):
    print "Cannot open file."
else:
    #Write to file
    for i in range(len(p)):
        out.write(p[i])

Example 18.15, Page Number: 441

In [12]:
import sys

n=[1,2,3,4,5]

#Open a file 'test'
out=open("test",'w')

#In case file cannot open
if(not(out)):
    print "Cannot open file."
else:
    #Write to file
    for i in range(5):
        out.write(chr(n[i]))
    out.close()
    
for i in range(5):         #clear array
    n[i]=0
    
#Open the file
In=open("test",'r')

#In case file cannot open
if(not(In)):
    print "Cannot open file."
else:
    #Read file
    for i in range(5):
        n[i]=ord(In.read(1))

#Result, shows value from file
for i in range(5):
    print n[i],
    
In.close()

1 2 3 4 5

Example 18.16, Page Number: 442

In [13]:
import sys
                                     
if not(len(sys.argv)==2):
    print "Usage: PR <filename>\n"
else:
    #Open a file
    In=open(sys.argv[1],'r')

    #In case file cannot open
    if(not(In)):
        print "Cannot open file."
    else:
        #Read file
        while True:
            ch=In.read(1)
            if not ch:
                break
            print ch,
    #Close file
    In.close()
                

Usage: PR <filename>

Example 18.17, Page Number: 443

In [14]:
 
out=open("test1",'w')
out.write("Hello")
out.close()
 
out=open("test2",'w')
out.write("There")
out.close()

 
f1=open("test1",'r')
 
if(not(In)):
    print "Cannot open file."

 
f2=open("test2",'r')
 
if(not(In)):
    print "Cannot open file."
    
print "Comparing files..."

buf1=f1.read()
buf2=f2.read()
print buf1,buf2

if len(buf1)==len(buf2):
    print "Files are of different sizes."
    f1.close()
    f2.close()
else:
    
    flag=1
    for i in range(len(buf1)):
        if not(buf1[i]==buf2[i]):
            print "Files differ."
            f1.close()
            f2.close()
            flag=0
            break
    if flag==1:
        print "Files are the same."
        
        

Comparing files...
Hello There
Files are of different sizes.

Example 18.18, Page Number: 445

In [15]:
print "Enter your name:"
 
str="hello world"

print str

Enter your name:
hello world

Example 18.19, Page Number: 447

In [2]:
 out=open("test",'r+b')
out.write("Hello")

 
if(not(out)):
    print "Cannot open file."
else:
    out.seek(2,0)
    out.write('X')
    out.close()

Example 18.20, Page Number: 447

In [3]:
 
out=open("test",'r+b')
out.write("Hello")
out.close()

In=open("test",'r')
 
if(not(In)):
    print "Cannot open file."
else:
    In.seek(2,0)
    ch=In.read()
    print ch
    

llo

Example 18.21, Page Number: 450

In [18]:
class three_d:
    def __init__(self,a,b,c):
        self.__x=a
        self.__y=b
        self.__z=c
    def __repr__(self):
        c=("%d"%self.__x)+", "+("%d"%self.__y)+", "+("%d"%self.__z)+"\n"
        return c 

 
a=three_d(1,2,3)
b=three_d(3,4,5)
c=three_d(5,6,7)
 
out=open("threed",'w')
 
if(not(out)):
    print "Cannot open file."
else:
    out.write(a.__repr__())
    out.write(b.__repr__())
    out.write(c.__repr__())