Python percent symbol in string

Python String formatting — percentage symbol after string substituion

The %s works when I don’t add a % within the single quotes immediately, but breaks when I add a % after that even with escaping. Is there a remedy for this, I can’t subsitute variables within an SQL query without this.

@Sreekiran’s answer is the best way to do it. If you really want to stick to your initial string formatting method, you need to do %s%% to get the % sign

@sysuser — if you are using python3.6 then you can use f-string also like query = f»select * from employees where employee_name like ‘%%'»

3 Answers 3

And this is how an SQL injection vulnerability is born. An SQL injection will let an intruder read private data, or even maybe modify data. Never ever pass a raw string into SQL query, unless you have made sure that it has no special characters such as ‘ , % , and \ . Actually, better to use a well tested function that does it for you.

query = "select * from employees where employee_name like '%s%%'" % (name) # (two `%%` at the end) 

solves your problems, but if somehow name == «%’ or » like ‘» (or something of the sort), then suddenly the query becomes:

"select * from employees where employee_name like '%' or '' like '%'" 

which will match all employees. Worse, even name = » is a nightmare in your case. I don’t think that using like in such queries is a good idea, to begin with.

For some information regarding formatting safely you can read stack-overflow questions under the sql-injection tag, such as Protecting against SQL injection in python. Every database system provides its own stored-procedure interface, please use it.

While your question in general is asking about the proper way to format a string in python, for your specific use case (this being a sql query), you should ensure that you are properly escaping your strings.

This is important for (1) stopping sql injection attacks, and (2) it is also helpful for when your variable-string has a quote in it.

For example, your current query will error for anyone with the name of O’Conner .

Instead, make use of your library’s parametrize methods for doing a query.

You don’t say which sql library you’re using, so I’ll give you an example with MySQLdb.

1) Basic example (without ‘%’ wildcard):

name = "O'Conner" query = ( "SELECT *" " FROM employees" " WHERE employee_name = %s" # notice the lack of quotes around %s ) params = (name,) cursor.execute(query, params) 

2) Since you’re using wildcards, you need to be more explicit:

query = ( "SELECT *" " FROM employees" " WHERE employee_name LIKE '<>%'" # must specify the quotes "".format( MySQLdb.escape_string(name).replace('%', '\\%').replace('_', '\\_') ) ) cursor.execute(query) 

(When you supply a params argument to cursor.execute , it is using MySQLdb.escape_string , behind the scenes. It also handles wrapping with quotes. Note that %s in case 1 is not a typical python %s, as opposed to case 2 — read the docs in the above link for more info.)

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Print Percentage Sign in Python

💡 Outline

To print percentage sign in Python, we can escape using the percentage sign twice instead of once.

See the code below:

Introduction

In this tutorial, we will see how to print percentage sign in python.

The modulus operator ( % ) or the percentage sign has multiple usages in Python. We use this operator to calculate the remainder for the division between two values for the arithmetic purpose.

We can also use the percentage sign for various string operations. We use it in string formatting and replacing values using format specifiers.

In the above example, we first find the remainder of 10 divided by 3 and store it in a variable a . Then, we have an integer in the print() function, which we display using the %d format specifier. There are different specifiers for different formats. The %s indicates a string, %f indicates float value, and more.

Print Percentage Sign in Python

Now we may think about what issue might arise while printing the percentage sign. If we print it normally, there seems to be no problem.

However, we get an error if we aim to print the percent sign ( % ) while using format specifiers.

In the above example, we can see that we wish to print 95.68% using the %s format specifier to provide the value from the string variable val in the print() function. We need to escape the percent sign to display it selectively.

Now let us understand how to escape percent sign in Python.

Using %% Character to Escape Percent Sign in Python

To print percentage sign, we can escape using the percentage sign twice instead of once.

By using the percentage sign twice ( %% ), we can overcome the error. However, if we are not using any specifier, this will print the percentage sign twice only.

Using the format() Function

The format() function can help us to format complex strings with ease. To escape the percent sign, we can place the string variable within curly braces and display the sign separately.

Using the f-String

The f-strings are a new addition to Python 3.6 and up and allow us to format strings faster and more efficiently. The format will be the same as discussed in the previous method.

In this article, we demonstrate the use and function of the percentage sign in Python. With the help of examples, we can understand the errors associated with printing the percent sign and how to overcome them. We also understand a little about string formatting, which is an essential technique in Python to get the result in our desired format.

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Python string formatting with percent sign

but it is syntax error. What would be the proper way of doing this without indexing like the first example?

it’s arguable whether it’s more «pythonic» but str.format would allow you to use *args expansion since it’s a method call

3 Answers 3

str % .. accepts a tuple as a right-hand operand, so you can do the following:

>>> x = (1, 2) >>> y = 'hello' >>> '%d,%d,%s' % (x + (y,)) # Building a tuple of `(1, 2, 'hello')` '1,2,hello' 

Your try should work in Python 3, where Additional Unpacking Generalizations is supported, but not in Python 2.x:

Actuall the extended iterable unpacking does not allow that syntax (python3.4): >>> ‘%d,%d,%s’ % (*x, y) File «», line 1 SyntaxError: can use starred expression only as assignment target Maybe it’ll be allowed by python3.5’s Additional Unpacking Generalizations

>>> x = (5,7) >>> template = 'first: <>, second: <>' >>> template.format(*x) 'first: 5, second: 7' 

Update:

For completeness I am also including additional unpacking generalizations described by PEP 448. The extended syntax was introduced in Python 3.5, and the following is no longer a syntax error:

>>> x = (5, 7) >>> y = 42 >>> template = 'first: <>, second: <>, last: <>' >>> template.format(*x, y) # valid in Python3.5+ 'first: 5, second: 7, last: 42' 

In Python 3.4 and below, however, if you want to pass additional arguments after the unpacked tuple, you are probably best off to pass them as named arguments:

>>> x = (5, 7) >>> y = 42 >>> template = 'first: <>, second: <>, last: ' >>> template.format(*x, last=y) 'first: 5, second: 7, last: 42' 

This avoids the need to build a new tuple containing one extra element at the end.

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