Hi,
I have a list of positive digits in a file. All I want to do is to add the negative sign (-) to each digit. Is there a code for this. eg list of digits
1 correspond -1
2 correspond-2
3 correspond -3 etc

The best way to do it is to read your file and write a new file with the negated digits. Could you be more specific about the content of your file (attach your file to a post ?).

Hi,
I have a list of positive digits in a file. All I want to do is to add the negative sign (-) to each digit. Is there a code for this. eg list of digits
1 correspond -1
2 correspond-2
3 correspond -3 etc

What about trying something similar to:

for i in range(1, 10):
print("-" + str(i))

you may replace range(1, 10) with a list (simple solution) or a generator of your choice (more sophisticated).

numarray = [1,2,-3,4,5,-25]
for n in numarray:
print "The inverse of", num, "is", num * -1
#print("The inverse of", num, "is", num*-1)
# use the above line if you're using python 3.x!

The output from the program is:

>>>
The inverse of 1 is -1
The inverse of 2 is -2
The inverse of -3 is 3
The inverse of 4 is -4
The inverse of 5 is -5
The inverse of -25 is 25
>>>

Since your numeric data comes from a file you will have strings, so you might as well use concatenation ...

# the test data
data = """\
123
44
72
27"""
fname = "numdata.txt"
# write the test file
fout = open(fname, "w")
fout.write(data)
fout.close()
# read the test file
for line in open(fname):
line = '-' + line.strip()
print(line)
"""my result -->
-123
-44
-72
-27
"""

If you need to do calculations with the data, convert with float().

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