什么时候需要在 Python 中的 integer 周围添加引号

Question

I just learnt that there is no quotation for integer in Python, but why is it needed in this case:

character_name = "Tom"
age = "50"
print("There once was a man named " + character_name + ",")
print("he was " + age + " years old.")

Answer 1

Using quotes to a digit, makes him become a string when it was an int (or float ) so it changes its values, you cannot do numerical operation on it anymore.

What you may need is the string representation of a number when concatenating it with other strings, here you may do

print("he was " + str(age) + " years old.")

Or, let print do it, by giving several parameters, and each one will be given its string representation

print("he was", age, "years old.")

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In resume, don't add quotes to a number when assigning it because it won't be a number anymore, handle it differently when you need but not as its beginning

Answer 2

You do not really need to do it if you use the format() method in Python 3, ie.:

character_name = "Tom"
age = 50
print("There once was a man named {}, he was {} years old.".format(character_name), age)

This is better in case you need to use the variable age in some equation later in the code.

Answer 3

when you use 2 strings and a “+” you concate them but when you use 2 numbers and a “+” you summarize them so if you use one string and one number and a “+” it gives you an error so you convert your number to a string

Valid Example 1: age = 30 name = “John” new_string = name + str(age)

Valid Example 2: age = “30” name = “John” new_string = age + name

invalid Example: age = 30 name = “John” new_string = name + age #Throws an issue