I want to be able to change a list of distances from miles to kms, where the list of miles is obtained in the below bit of code:
input_string = input("Enter a list of distances, separated by spaces").strip()
To change the list of inputs into a list of integers, I used:
distances = input_string.split()
print("This is what you entered: ")
for distance in distances:
print(distance)
def str2int(word):
"""Converts the list of string of miles into a list of integers of miles"""
integer = int(word)
if int(word):
return integer
else:
sys.exit("Please try again and enter a list of integers.")
def validate_all(distances):
"""
Checks if all the inputs are integers. If not all are integers, sys.exit
without converting any of the distances and ask to try again.
"""
true_list = []
for distance in distances:
if str2int(distance):
true_list.append(distance)
if len(distances) == len(true_list):
return True
else:
return False
print("And now, we are going to convert the first one to kilometers:")
miles = distances[0]
if validate_all:
# now, the calculation and display
kms = miles_int * KMPERMILE
print("The first distance you entered, in kilometers:", kms)
for i in range(1, len(distances), 1):
miles_int = str2int(distances[i])
kms = miles_int * KMPERMILE
print("The next distance you entered in kilometres:", kms)
BUT, when I try to check if all elements of the list of strings are able to be changed into an integer (with validate_all(word)) and have something like
12 23 apples banana 5
as my input, the program crashes saying that there is a value error at
str2int(word)
-> if int(word):
instead of me getting the sys.exit
Can anyone debug this for me/get this right for me please?
-
1Can you post the error stack trace, please?Christian Tapia– Christian Tapia2014年01月08日 04:05:10 +00:00Commented Jan 8, 2014 at 4:05
4 Answers 4
>>> t = '12 23 apples banana 5'
>>> [int(x) for x in t.split() if x.isdecimal()]
[12, 23, 5]
Comments
You could use a try-except clause:
def str2int(word):
"""Converts the list of string of miles into a list of integers of miles"""
try:
integer = int(word)
return integer
except ValueError:
print "here"
sys.exit("Please try again and enter a list of integers.")
print(str2int("asd"))
Output:
here
Please try again and enter a list of integers.
Note:
You can read more about Handling Exceptions and the try-except clauses in the Python docs.
Comments
You tried doing if int(x): ..., but int is not a predicate. If x is a string which cannot be converted to an int, a ValueError is raised. If x='0' for example, if int(x): ... is evaluated to False, despite being an int-like value.
What you need is the following predicate:
def is_int_able(x):
try:
int(x)
return True
except ValueError:
return False
With this, you can do:
[ int(x) for x in line.split() if is_int_able(x) ]
Comments
Your validate_all() could make use of all() and str.digit():
In [1]: all(e.isdigit() for e in ['12', '23', 'apples', 'banana', '5'])
Out[1]: False
In [2]: all(e.isdigit() for e in ['12', '23', '5'])
Out[2]: True
But perhaps a better way would be to do away with this validation and employ the if filtering in a list comprehension:
In [3]: distances = ['12', '23', 'apples', 'banana', '5']
In [4]: [int(km) * km_to_miles for km in distances if km.isdigit()]
Out[4]: [7.456454304, 14.291537416, 3.10685596]
Comments
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