This question already has answers here:
What does the $ symbol do in VBA?
(5 answers)
Closed 4 years ago.
Is there any difference between using a builtin function returning a string such as Left or using the same function with a $ appended (Left$)?
The output of this:
Debug.Print Left("Foo", 2)
Debug.Print Left$("Foo", 2)
is always
Fo
Fo
I suspect that it's strictly the same thing and that the $ versions exist only for some compatibility reasons.
The typed functions (those ending with a $) return a String. The un-typed versions return a Variant. Internally, these are handled by a pair of different functions (in the case of Left, it is _B_str_Left and _B_var_Left).
If you are assigning the return value to a String or a parameter expecting a String, using the typed version (Left$) avoids an implicit cast to a Variant. Similarly, if you're assigning to a Variant, using the un-typed version avoids a cast.
Left$() wants a string as argument but Left() expects a variant. Therefore using Left$() is faster if you know you will always pass it a string.
Related
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What does "list comprehension" and similar mean? How does it work and how can I use it?
(5 answers)
Closed 3 years ago.
I have scoured the internet and I cannot find any reference to this type of for loop:
variable = [(item["attribute1"], item["attribute2]") for item in piece_of_json_data]
I am using this to update wtform's SelecField choices:
form.SelectField.choices = variable
but I can only get it to work if I replace one of the attributes in parenthesis with a static number:
variable = [(1, item["attribute2"]) for item in piece_of_json_data]
but that sets the value of the option field to "1", when I need the option values to be one of the attributes as a string.
Does this create a dict? a tuple? is there some kind of terminology for this that I can use to find documentation?
Thanks to the comments, I now understand that I am using list comprehension to create a tuple. The tuple works fine with both string and integer values. My issue has to do with .choices not accepting a string.
I found that my only problem is that I had coerce set to int on my selectfield, so naturally it wanted an integer.
Trying to understand how "%s%s" %(a,a) is working in below code I have only seen it inside print function thus far.Could anyone please explain how it is working inside int()?
a=input()
b=int("%s%s" %(a,a))
this "%s" format has been borrowed from C printf format, but is much more interesting because it doesn't belong to print statement. Note that it involves just one argument passed to print (or to any function BTW):
print("%s%s" % (a,a))
and not (like C) a variable number of arguments passed to some functions that accept & understand them:
printf("%s%s,a,a);
It's a standalone way of creating a string from a string template & its arguments (which for instance solves the tedious issue of: "I want a logger with formatting capabilities" which can be achieved with great effort in C or C++, using variable arguments + vsprintf or C++11 variadic recursive templates).
Note that this format style is now considered legacy. Now you'd better use format, where the placeholders are wrapped in {}.
One of the direct advantages here is that since the argument is repeated you just have to do:
int("{0}{0}".format(a))
(it references twice the sole argument in position 0)
Both legacy and format syntaxes are detailed with examples on https://pyformat.info/
or since python 3.6 you can use fstrings:
>>> a = 12
>>> int(f"{a}{a}")
1212
% is in a way just syntactic sugar for a function that accepts a string and a *args (a format and the parameters for formatting) and returns a string which is the format string with the embedded parameters. So, you can use it any place that a string is acceptable.
BTW, % is a bit obsolete, and "{}{}".format(a,a) is the more 'modern' approach here, and is more obviously a string method that returns another string.
This question already has answers here:
What is the purpose of the single underscore "_" variable in Python?
(5 answers)
Trying to understand Python loop using underscore and input
(4 answers)
Closed 4 years ago.
I was check a solution on hacker rank where i was solving a question asking to print the name of the person with the second highest score from an input which has to be converted to a nested list first .
I understood all the logic in the code and most part of the code but why the Underscore ( _ ) in the for loop .Please explain me the code if there is a different concept .
marksheet = []
for _ in range(0,int(input())):
marksheet.append([input(), float(input())])
second_highest = sorted(list(set([marks for name, marks in marksheet])))[1]
print('\n'.join([a for a,b in sorted(marksheet) if b == second_highest]))
It's a Pythonic convention to use underscore as a variable name when the returning value from a function, a generator or a tuple is meant to be discarded.
In your example, the code inside the for loop does not make any use of the values generated by range(0,int(input())), so using an underscore makes sense as it makes it obvious that the loop does not intend to make use of it.
This question already has answers here:
Why can't variable names start with numbers?
(24 answers)
Closed 8 years ago.
In many languages (C#, Javascript, CSS, and so on) I can't declare this variable:
123test
but I can declare this:
test123
What's the real cause of it?
It simplifies the parser. It can tell from the first character in a token whether it's an identifier or a number.
Also, the syntax for floating point can look like this:
123e45
This means 123x1045. If identifiers could start with a number, this could be confused with a variable.
There are some languages that don't have this prohibition, Common Lisp for instance. It's rule is essentially that the token is a symbol unless it can be parsed as a number. Since it also allows the input radix to be customized, it has the property that whether a token is a number or symbol depends on the setting of a variable (it also has escaping mechanisms that allow you to force it one way or the other).
Because then a string of digits would be a valid identifier as well as a valid number.
int 17 = 497;
int 42 = 6 * 9;
String 1111 = "Totally text";
#skiphoppy`s answear.
More information: Why can't variable names start with numbers?
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Annoying PHP error: “Strict Standards: Only variables should be passed by reference in”
I have this line of code,
$extension=end(explode(".", $srcName));
when I fun my function I get
PHP Strict Standards: Only variables should be passed by reference in
I am not sure how to solve this
The function end() requires a variable to be passed-by-reference and passing the return-value of a function doesn't acheive this. You'll need to use two lines to accomplish this:
$exploded = explode(".", $srcName);
$extension = end($exploded);
If you're simply trying to get a file-extension, you could also use substr() and strrpos() to do it in one line:
$extension = substr($srcName, strrpos($srcName, '.'));
Or, if you know the number of .'s that appear in the string, say it's only 1, you can use list() (but this won't work if there is a dynamic number of .'s:
list(,$extension) = explode('.', $srcName);