How do I put a variable’s value inside a string?
PythonStringVariablesPython Problem Overview
I would like to put an int into a string. This is what I am doing at the moment:
num = 40
plot.savefig('hanning40.pdf') #problem line
I have to run the program for several different numbers, so I'd like to do a loop. But inserting the variable like this doesn't work:
plot.savefig('hanning', num, '.pdf')
How do I insert a variable into a Python string?
Python Solutions
Solution 1 - Python
Oh, the many, many ways...
String concatenation:
plot.savefig('hanning' + str(num) + '.pdf')
Conversion Specifier:
plot.savefig('hanning%s.pdf' % num)
Using local variable names:
plot.savefig('hanning%(num)s.pdf' % locals()) # Neat trick
Using str.format():
plot.savefig('hanning{0}.pdf'.format(num)) # Note: This is the preferred way since 3.6
Using f-strings:
plot.savefig(f'hanning{num}.pdf') # added in Python 3.6
This is the new preferred way:
Using string.Template:
plot.savefig(string.Template('hanning${num}.pdf').substitute(locals()))
Solution 2 - Python
plot.savefig('hanning(%d).pdf' % num)
The % operator, when following a string, allows you to insert values into that string via format codes (the %d in this case). For more details, see the Python documentation:
https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
Solution 3 - Python
With the introduction of formatted string literals ("f-strings" for short) in Python 3.6, it is now possible to write this with a briefer syntax:
>>> name = "Fred"
>>> f"He said his name is {name}."
'He said his name is Fred.'
With the example given in the question, it would look like this
plot.savefig(f'hanning{num}.pdf')
Solution 4 - Python
Not sure exactly what all the code you posted does, but to answer the question posed in the title, you can use + as the normal string concat function as well as str().
"hello " + str(10) + " world" = "hello 10 world"
Hope that helps!
Solution 5 - Python
In general, you can create strings using:
stringExample = "someString " + str(someNumber)
print(stringExample)
plot.savefig(stringExample)
Solution 6 - Python
If you would want to put multiple values into the string you could make use of format
nums = [1,2,3]
plot.savefig('hanning{0}{1}{2}.pdf'.format(*nums))
Would result in the string hanning123.pdf. This can be done with any array.
Solution 7 - Python
I had a need for an extended version of this: instead of embedding a single number in a string, I needed to generate a series of file names of the form 'file1.pdf', 'file2.pdf' etc. This is how it worked:
['file' + str(i) + '.pdf' for i in range(1,4)]
Solution 8 - Python
You can make dict and substitute variables in your string.
var = {
"name": "Abdul Jalil",
"age": "22"
}
temp_string = """
My name is %(name)s.
I am %(age)s years old.
""" % var
Solution 9 - Python
You just have to cast the num varriable into a string using
str(num)