CODEWITHSUNDEEP
pythonpython-2.7
user2950680
user2950680

Reputation: 517

Why does %r work while %d does in some cases even though there is a number

Python Beginner here. Would like to ask you a very simple question.

This is the first sample code :-

print "I will \"Add\" any two number that you type."
x = raw_input("What is the first number?")
y = raw_input("What is the second number?")

z = x + y

print "So, %d plus %d equals to %d" % (x, y, z)

Using %d in the last line gives me the error :

   TypeError: %d format: a number is required, not str

This is the second sample code :-

print "I will \"Add\" any two number that you type."
x = raw_input("What is the first number?")
y = raw_input("What is the second number?")

z = x + y

print "So, %r plus %r equals to %r" % (x, y, z)

This does not give the error that the first code gave.

So my question is why using %d gives me the error but using %r does not give me the error ?

Upvotes: 1

Views: 96

Answers (4)

Vynce
Vynce

Reputation: 3236

per https://docs.python.org/2/library/functions.html#raw_input raw_input takes your input and assigns it as a string.

%d only formats numbers.

per https://docs.python.org/2/library/string.html#format-specification-mini-language (hard to find, %r is not well documented) %r uses convert_field to convert the variable into a representation that will get the same value if parsed.

I believe the + is coercing the two strings (x and y) into numbers so they can be added.

Upvotes: 0

Anand S Kumar
Anand S Kumar

Reputation: 90919

When you take input through raw_input() , it returns you a string, so x and y are strings, and z is the concatenation of x and y , not its addition. Not sure if that is what you intended. If you want them as int , convert them to int by using int(raw_input(...)) .

The error you get is because %d expects x, y and z (used to replace %d ) to be integers (But they are actually strings, hence the error).

Whereas %r which means the output of repr() which accepts any kind of objects, and hence it works in your second case, though it would be returning the concatenation (not addition) .

Upvotes: 1

Victor Santiago
Victor Santiago

Reputation: 30

When you use raw_input you then have to convert the strings to the data type you want for example on my example 1 I am converting the variables x and y to data type int using the int() function. Or you can just use input and Python will take care of that for you for example if on input you enter a number Python will assume is an integer and if you type a string then it will assume is a string.

##Example 1:
print "I will \"Add\" any two number that you type."
x = raw_input("What is the first number?")
y = raw_input("What is the second number?")

z = int(x) + int(y)

print "So, %d plus %d equals to %d" % (int(x), int(y), z)

##Example 2:
print "I will \"Add\" any two number that you type."
x = input("What is the first number?")
y = input("What is the second number?")

z = x + y

print "So, %d plus %d equals to %d" % (x, y, z)

Upvotes: 0

yxre
yxre

Reputation: 3704

Every variable has an implicit type that is not declared. A type is a number or string(text). raw_input always returns a string.

The %d flag tries to format the variable into a number. When it finds text, it throws an error.

Upvotes: 0

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