I am reading only the first line in Python using:
with open(file_path, 'r') as f:
my_count = f.readline()
print(my_count)
I am a little confused about the scope of the my_count
variable. Although the print statement works fine, wouldn't it be better to do something like my_count = 0
outside the with
statement first (e.g., in C I would do int my_count = 0
)?
A with
statement does not create a scope (like if
, for
and while
do not create a scope either).
As a result, Python will analyze the code and see that you made an assignment in the with
statement, and thus that will make the variable local (to the real scope).
In Python variables do not need initialization in all code paths: as a programmer, you are responsible to make sure that a variable is assigned before it is used. This can result in shorter code: say for instance you know for sure that a list contains at least one element, then you can assign in a for
loop. In Java assignment in a for
loop is not considered safe (since it is possible that the body of the loop is never executed).
Initialization before the with
scope can be safer in the sense that after the with
statement we can safely assume that the variable exists. If on the other hand the variable should be assigned in the with
statement, not initializing it before the with
statement actually results in an additional check: Python will error if somehow the assignment was skipped in the with
statement.
A with statement is only used for context management purposes. It forces (by syntax) that the context you open in the with
is closed at the end of the indentation.