Python if statement not executing

Question

#   TEST
import sys  
a=sys.stdin.readline()    # here the user inputs the string "HELLO"  
print a
if a == "HELLO":  
    sys.stdout.write("GOOD_BYE")  
print "AAAAAAAAAAA"  
raw_input('\npress any key to continue')

Hi there. I am new to Python.
I am using Python 2.7.11.
I do not understand why control is not entering the if statement.
The output for the given code comes out as

HELLO  
HELLO   
AAAAAAAAAAA
press any key to continue

NOTE: The first "HELLO" above is user input
I've tried sys.stdout.flush() for the sys.stdout.write() statement. But it doesn't seem to help.
If I write the same code with a=raw_input() instead of the second line, it works perfectly fine.
Can anyone explain the reason for this.

Vj- · Accepted Answer · 2018-04-02 06:40:22Z

2

readline comes with a newline character at the end. So what you are actually doing is comparing

HELLO\n == HELLO

which is actually false.

Do a.rstrip() to remove newline.

answered Apr 2, 2018 at 6:40

Vj-

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Comments

Sangam Belose · Accepted Answer · 2018-04-02 06:48:40Z

0

readline() function read newline character from standard input console. Please use rstrip("\n") to remove the same.

import sys  
a=sys.stdin.readline().rstrip('\n')
print (a)
if a == "HELLO":  
    sys.stdout.write("GOOD_BYE")  
print ("AAAAAAAAAAA")
raw_input('\npress any key to continue')

answered Apr 2, 2018 at 6:48

Sangam Belose

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Comments

Abhijit Saxena · Accepted Answer · 2018-04-02 06:53:13Z

0

Try using 'in' instead of '==' in your if condition, sometimes the lines might have some hidden characters.

if "HELLO" in a:

answered Apr 2, 2018 at 6:53

Abhijit Saxena

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Comments

Pankaj Kumar · Accepted Answer · 2018-04-02 07:16:42Z

0

You are pressing 'ENTER' after input string to send input. So your input is 'HELLO\n' while your if statement 'if' condition is 'a == "HELLO"'.

Use strip() method. The method strip() returns a copy of the string in which all chars have been stripped from the beginning and the end of the string (default whitespace characters).

So new working code :

import sys  
a=sys.stdin.readline().rstrip('\n')
a=a.strip() # This will remove \n from input
print (a)
if a == "HELLO":  
    sys.stdout.write("GOOD_BYE")  
print ("AAAAAAAAAAA")
raw_input('\npress any key to continue')

answered Apr 2, 2018 at 7:16

Pankaj Kumar

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