This question already has an answer here:
How can I concatenate str and int objects?
(1 answer)
Closed 1 year ago.
I'm new to Python, so I've been running through my own set of exercises to simply start memorizing basic functions and syntax.
I'm using the PyCharm IDE and Python 3.4. I've run into an issue when running through some basic string and integer concatenation exercises. Each instance below is throwing an unsupported operand type. There are several threads on Stack Overflow that clearly states proper concatenation syntax, but the above error message continues to plague me.
print ("Type string: ") + str(123)
print ("Concatenate strings and ints "), 10
In Python 3+, print is a function, so it must be called with its arguments between parentheses. So looking at your example:
print ("Type string: ") + str(123)
It's actually the same as:
var = print("Type string: ")
var + str(123)
Since print returns nothing (in Python, this means None), this is the equivalent of:
None + str(123)
which evidently will give an error.
That being said about what you tried to do, what you want do to is very easy: pass the print function what you mean to print, which can be done in various ways:
print ("Type string: " + str(123))
# Using format method to generate a string with the desired contents
print ("Type string: {}".format(123))
# Using Python3's implicit concatenation of its arguments, does not work the same in Python2:
print ("Type string:", str(123)) # Notice this will insert a space between the parameters
Note that print is a function in Python 3. In Python 2, your first line would concatenate "Type string: " and "123" and then print them. In Python 3, you are calling the print function with one argument, which returns None, and then add "123" to it. That doesn't make any sense.
The second line doesn't generate an error in Python 2 or 3 (I've tested it with 2.7.7 and 3.2.3). In Python 2, you get
Concatenate strings and ints 10
while in Python 3, your script should only print
Concatenate strings and ints
This is because again, print is a function, and therefore you call it with the argument "Concatenate strings and ints". The , 10 makes your line a tuple of the return value of print, which is None, and 10. Since you don't use that tuple for anything, there is no visible effect.
Try format():
print("Type string: {}".format(123))
print("Concatenate strings and ints {}".format(10))
There is nothing wrong with this:
print ("Type string: ") + str(123)
print is just a function like anything else. And you're calling that function with one argument, "Type string: ", and then trying to add the result (which will be None) to the string '123'. That isn't going to work. If you wanted to add the two strings together, you have to put them into the same expression, inside the parentheses:
print("Type string: " + str(123))
Similarly:
print ("Concatenate strings and ints "), 10
This calls print with one argument, and then makes a tuple of the None returned by print and the number 10. If you want to pass 10 to the print call, it has to go inside the parentheses:
print("Concatenate strings and ints ", 10)
As gitaarik's answer points out, using str.format is more flexible, and avoids the possibility of problems like this. It also gives you code that works exactly the same way in both Python 2.6-2.7 and Python 3.x, which is pretty nice even if you aren't trying to write dual-platform/single-codebase code, because it'll be understandable even to people who only know one or the other.
I think this is a pretty cool way to concatenate a string and an int in Python:
print (f"Type string: {123}")
print (f"Concatenate strings and ints {10}")
You can do it like this:
c = 'Emerson'
d = 32
print("My name is %s and I am %d years old." %(c,d))
Result:
My name is Emerson and I am 32 years old.
Related
This question already has an answer here:
How can I concatenate str and int objects?
(1 answer)
Closed 3 years ago.
I am unable to place an integer inside my print statement alongside a string, and concatenate them together.
pounds = input("Please type in your weight in pounds: ")
weight = int(pounds) * 0.45
print("You " + weight)
I thought that I would be able to put these together, why am I unable to?
Python doesn't let you concatenate a string with a float. You can solve this using various methods:
Cast the float to string first:
print("You " + str(weight))
Passing weight as a parameter to the print function (Python 3):
print("You", weight)
Using various Python formatting methods:
# Option 1
print("You %s" % weight)
# Option 2 (newer)
print("You {0}".format(weight))
# Option 3, format strings (newest, Python 3.6)
print(f"You {weight}")
Since you are trying to concat a string with an integer it's going to throw an error. You need to either cast the integer back into a string, or print it without concatenating the string
You can either
a) use commas in the print function instead of string concat
print("You",weight)
b) recast into string
print("You "+str(weight))
Edit:
Like some of the other answers pointed out, you can also
c) format it into the string.
print("You {}".format(weight))
Hope this helps! =)
print("You %s" % weight) or print("You " + str(weight))
Another way is to use format strings like print(f"You {weight}")
Python is dynamically typed but it is also strongly typed. This means you can concatenate two strs with the + or you can add two numeric values, but you cannot add a str and an int.
Try this if you'd like to print both values:
print("You", weight)
Rather than concatenating the two variables into a single string, it passes them to the print function as separate parameters.
This question already has answers here:
How can I concatenate str and int objects?
(1 answer)
String formatting: % vs. .format vs. f-string literal
(16 answers)
Closed 7 months ago.
I have to write a program that reads in a whole number and prints out that number divided by two. This is my code:
a= int(input("Number: "))
h= a/2
print("Half number: " + h)
But I keep getting this
Number: 6
Traceback (most recent call last):
File "program.py", line 3, in <module>
print("Half number: " + h)
TypeError: Can't convert 'float' object to str implicitly
I don't see anything wrong with my code and I have no idea what the error is. Any idea what's wrong?
The expression:
"Half number: " + h
is trying to add a string to a float. You can add strings to strings:
"This string" + ", then this string"
and floats to floats:
100.0 + 16.8
but Python isn't willing to let you add strings and floats. (In the error message above, Python has processed the first string and the addition, and it now expects a string -- that's why you get the error that it can't -- or at least won't -- convert a 'float' number to a string.)
You can tell Python this is what you really want it to do in a few ways. One is to use the built-in str() function which converts any object to some reasonable string representation, ready to be added to another string:
h = 100
"You can add a string to this: " + str(h)
a= int(input("Number: "))
h= a/2
print('Half number:', h)
Without the spaces in between though
Here is a very simple way to do it.
Here's a sample solution from Grok Learning:
n = int(input('Number: '))
print('Half number:', n/2)
Here's my explanation below:
As you might've already guessed, n here is a variable. And in this code, we will be assigning some information to n. int(input('Number ')) is the statement that Python will then read, and follow. int() tells Python that the input will be an integer, and input() allows the user to input whatever they would like to input. n/2 is simply another way of saying "n divided by two". print() tells Python to print a statement, and so print('Half number:', n/2) will print out that "Half number" is simply just half of the number entered above.
Here's an example of what the output should look like:
Number: 6
Half number: 3
(In that example, the input was 6.)
So, yes, I know that you may already know this stuff but I am leaving this information for people who may visit this website in the future. The error that you had was that you used a +, when you should've used a ,. Python is pretty strict when it comes to processing what you're saying, so it didn't allow you to put a str and an int together using a +. So next time, remember to use a ,.
I hope this helps you.
This question already has answers here:
How can I read inputs as numbers?
(10 answers)
Closed 7 months ago.
My goal is very simple, which makes it all the more irritating that I'm repeatedly failing:
I wish to turn an input integer into a string made up of all numbers within the input range, so if the input is 3, the code would be:
print(*range(1, 3+1), sep="")
which obviously works, however when using an n = input() , no matter where I put the str(), I get the same error:
"Can't convert 'int' object to str implicitly"
I feel sorry to waste your collective time on such an annoyingly trivial task..
My code:
n= input()
print(*range(1, n+1), sep="")
I've also tried list comprehensions (my ultimate goal is to have this all on one line):
[print(*range(1,n+1),sep="") | n = input() ]
I know this is not proper syntax, how on earth am I supposed to word this properly?
This didn't help, ditto this, ditto this, I give up --> ask S.O.
I see no reason why you would use str here, you should use int; the value returned from input is of type str and you need to transform it.
A one-liner could look like this:
print(*range(1, int(input()) + 1), sep=' ')
Where input is wrapped in int to transform the str returned to an int and supply it as an argument to range.
As an addendum, your error here is caused by n + 1 in your range call where n is still an str; Python won't implicitly transform the value held by n to an int and perform the operation; it'll complain:
n = '1'
n + 1
TypeErrorTraceback (most recent call last)
<ipython-input-117-a5b1a168a772> in <module>()
----> 1 n + 1
TypeError: Can't convert 'int' object to str implicitly
That's why you need to be explicit and wrap it in int(). Additionally, take note that the one liner will fail with input that can't be transformed to an int, you need to wrap it in a try-except statement to handle that if needed.
In your code, you should just be able to do:
n = int(input())
print(*range(1,n+1),sep="")
But you would also want to have some error checking to ensure that a number is actually entered into the prompt.
A one-liner that works:
print(*range(1, int(input()) + 1), sep="")
This question already has answers here:
Taking String arguments for a function without quotes
(2 answers)
Closed 6 years ago.
I am trying to define a simple function which checks if what the user placed into the arguments equal the letter B (No reason. Just made it B.) This is my code:
def letter_check_B(letter):
letter = str(letter)
if letter == 'B':
print("You entered B")
else:
print("You did not enter B")
However, when using the above code, by typing in:
letter_check_B(B)
I get an error stating:
NameError: name 'B' is not defined
How would I go about to fix this without changing how the overall code works. I want to be able to make this code work by placing the letter into the argument (if that is possible).
You can't use a plain B as a value in Python. The syntax will always see that as a variable reference. Since you haven't ever assigned anything to the name B, you get a NameError exception.
The str() function can only work on values; it'll work on an integer for example:
>>> str(1)
'1'
You could create a string value with a string literal expression:
>>> 'B'
'B'
Passing that to the str() function is a no-op (the same string value is returned again):
>>> str('B')
'B'
but it'd make your function work nonetheless:
>>> letter_check_B('B')
You entered B
Note that any method you'd use to get user input, would return a value anyway. The input() function for example, returns an object (value) of type str:
>>> input('Enter a letter: ')
Enter a letter: B
'B'
>>> type(_) # what is the type of the value produced by the last expression?
<class 'str'>
You may want to read up on getting and validating user input, see Asking the user for input until they give a valid response
B is a name (the Python word for a variable); and 'B' is a string with one character.
Since you didn't define B, Python is telling you that you are trying to pass a name that isn't defined.
Note the quotes 'B' make a difference here. You need to pass a string, like this:
letter_check_B('B')
You should read up on the string type.
I am learning Python and here is an example of some code :
When would you use this :
Y = "Apple"
print "The object is an %s" % Y
And when would you use this?
X = "Grape"
print "The object is an " , X
And why?
The difference goes beyond just convenience and preference. The two methods are two different things.
Let's consider print "The object is an " , X first. The print statement in Python 2 is a bit irregular and unintuitive in its behavior, which is one of the reasons why Python 3 has a print function instead. In Python 2, the statement takes comma-separated expressions, and prints them out one by one, converting them to strings if necessary, and using a few rules to decide whether to put a space before each expression (it puts a space except "(1) when no characters have yet been written to standard output, (2) when the last character written to standard output is a whitespace character except ' ', or (3) when the last write operation on standard output was not a print statement.")
So when you have strings X and Y, and do print X,Y, it prints X and then Y, probably with whitespace in between. If you want to print a bunch of things quickly, this works well. It's to some extent an easy shorthand for combining separate strings as well. It just prints string representations of the expressions you put in, however. Unless you've already converted the objects to the string you want them to be, you don't have any control over what they look like. It is also something that's specific to the print statement.
The % operation for string formatting, on the other hand, is its own thing; you don't need to use it with print. You can also do things like a = "The object is an %s." % X, and it will work as expected, substituting in the X. But that's not all it can do, or it wouldn't be called string formatting. Instead, it allows you to control how things are put into the string, especially for numbers. This makes it more generally useful, even if the usage is a bit opaque, and reading the documentation on it is a good idea. But, as some examples:
In [1]: a = 1507.2515621
In [2]: print "a is: %d" % a # print as a signed integer
a is: 1507
In [3]: print "a is: %f" % a # print as a float, decimal format
a is: 1507.251562
In [4]: print "a is: %10.2E" % a # print as a float in exponential format, with
a is: 1.51E+03
In [5]: print "a is: %x" % a # signed hexadecimal
a is: 5e3
In [6]: print "The object is an %s." % "Apple" # a string using str()
The object is an Apple.
In [7]: print "The object is an %r." % "Apple" # a string using repr()
The object is an 'Apple'.
In [19]: z = {'a': 2, 'b': 3}
In [21]: print "a is %(a)d, and b is %(b)d." % z
a is 2, and b is 3.
You should be aware, however, that % formatting is no longer considered the "correct" way to do string formatting, and it isn't in Python 3 at all. Instead, both Python 2.6 and up, and Python 3 have the .format method on strings, which is less compact, but fits the rest of python much better (% is actually an overloaded modulo operator). As some examples:
In [39]: print "a is: {0}, or {0:g}, or {0:e}, and z is {1:s},\n and a in z is {1[a]}, \
....: but the a variable is {0:,}.".format(a,z)
a is: 1507.2515621, or 1507.25, or 1.507252e+03, and z is {'a': 2, 'b': 3},
and a in z is 2, but the a variable is 1,507.2515621.
This has many options, and I'd highly recommend reading the documentation on it. Unfortunately, it has what I feel are some unfortunate design choices, and the documentation is rather opaque.
A better example of when you would use the first method (percent formatting) would be
Y = 'Apple'
print "The %s tastes sweet." % Y
It allows you to easily insert variables into a string without having to do something like this:
Y = 'Apple'
print "The", Y, " tastes sweet."
So it's personal preference really, but percent formatting allows one to insert variables into a string without concatenation.
The former prints a single, formatted string. The latter prints two things, one after the other, separated by a space. Use string formatting when you want to put together a string, such as for use in a GUI element or as an argument to some processing function. Sending multiple objects to the print statement (or to the print() function in Python 3) is mostly for print debugging (although there's nothing wrong with using it in a command-line program, if the resulting code is as clear as what you'd create with string formatting).