Create Python string placeholder (%s) n times - string

Question

I am looking to automatically generate the following string in Python 2.7 using a loop based on the number of columns in a Pandas DataFrame:
INSERT INTO table_name (firstname, lastname) VALUES (534737, 100.115)
This assumes that the DataFrame has 2 columns.
Here is what I have:
# Generate test numbers for table:
df = pd.DataFrame(np.random.rand(5,2), columns=['firstname','lastname'])
# Create list of tuples from numbers in each row of DataFrame:
list_of_tuples = [tuple(x) for x in df.values]
Now, I create the string:
Manually - this works:
add_SQL = INSERT INTO table_name (firstname, lastname) VALUES %s" % (list_of_tuples[4])
In this example, I only used 2 column names - 'firstname' and 'lastname'. But I must do this with a loop since I have 156 column names - I cannot do this manually.
What I need:
I need to automatically generate the placeholder %s the same
number of times as the number of columns in the Pandas DataFrame.
Here, the DataFrame has 2 columns so I need an automatic way to
generate %s twice.
Then I need to create a tuple with 2 entries,
without the ''.
My attempt:
sss = ['%s' for x in range(0,len(list(df)))]
add_SQL = "INSERT INTO table_name (" + sss + ") VALUES %s" % (len(df), list_of_tuples[4])
But this is not working.
Is there a way for me to generate this string automatically?

Answer 1

Here is what I came up with - it is based on dwanderson's approach in the 2nd comment of the original post (question):
table_name = name_a #name of table
# Loop through all columns of dataframe and generate one string per column:
cols_n = df.columns.tolist()
placeholder = ",".join(["%s"]*df.shape[1]) #df.shape[1] gives # of columns
column_names = ",".join(cols_n)
insrt = "INSERT INTO %s " % table_name
for qrt in range(0,df.shape[0]):
add_SQL_a_1 = insrt + "(" + column_names + ") VALUES (" + placeholder + ")" #part 1/2
add_SQL_a_2 = add_SQL_a_1 % list_of_tuples[qrt] #part 2/2
This way, the final string is in part 2/2.
For some reason, it would not let me do this all in one line and I can't figure out why.