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Just your personal preference, which do you prefer?
if filename in filesAndFoldersList:
while a != "TEST":
a = input("Input: ")
Or
if(filename in filesAndFoldersList):
while(a != "TEST"):
a = input("Input: ")
Either one works, so this is just personal preference I think. Second one is more similar to Java/C++. But which you do prefer and why?
You should never use parentheses directly after the keyword of a statement, as you do in your second style. You are confusing the reader by making it look like they are functions. All you are doing is group the expression in parentheses, Python will ignore these and all you have achieved is the removal of the space after the keyword.
Neither can you use the style with all compound statements; you cannot use the style with a for loop or a with statement that includes the as <target> clause.
The Python Style Guide makes no mention of the second (parenthesized) style, at all; it makes the assumption that no-one would use it.
Note that this is separate from using parentheses around long expressions, where you use (...) around the if condition expression if it is otherwise too long to fit on a single line. In such a situation you want to put a space between the opening ( and the if keyword:
if (
this_is_one_thing and
that_is_another_thing or
(more_conditions and such_things)
):
do_something()
Related
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I am trying to detect if a string contains any element in an array. I want to know if the string(msg) has any element from the array(prefixes) in it.
I want this because I want to make a discord bot with multiple prefixes, heres my garbage if statement.
if msg.startswith(prefixes[any]):
The existing answers show two ways of doing a linear search, and this is probably your best choice.
If you need something more scalable (ie, you have a lot of potential prefixes, they're very long, and/or you need to scan very frequently) then you could write a prefix tree. That's the canonical search structure for this problem, but it's obviously a lot more work and you still need to profile to see if it's really worthwhile for your data.
Try something like this:
prefixes = ('a','b','i')
if msg.startswith(prefixes):
The prefixes must be tuple because startswith function does not supports lists as a parameter.
There are algorithms for such a search, however, a functional implementation in Python may look like this:
prefixes = ['foo', 'bar']
string = 'foobar'
result = any(map(lambda x: string.startswith(x), prefixes))
If you search for x at any position in string, then change string.startswith(x) to x in string.
UPDATE
According to #MisterMiyagi in comments, the following is a more readable (possibly more efficient) statement:
result = any(string.startswith(prefix) for prefix in prefixes)
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I need to pass a variable '3-123' to a method in python, but if I do str(3-123) I get '-120'. Tried iterating, but I got an error cause it's an int.
You simply pass the string "3-123".
Your expression str(3-123) tells Python to first evaluate what is in parentheses, which is very clearly the arithmetic expression 3-123. That evaluation mandates a subtraction.
UPDATE PER USER COMMENT
Since you just got it returned from REST, then it's already a string. It seems that your problem is that you're building an expression string to be evaluated in SQL. In this case, you need to build the string you're going to send to SQL, at the character level. For this one item you would extend your 3-123 string with quotation marks:
from_rest = "3-123" # In practice, this comes directly from your REST return value.
to_sql = '"' + from_rest + '"'
This leaves you with a variable that contains the string "3-123" -- seven characters, rather than the original five.
Is that what you needed?
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I am trying to parse some open-source code of Python to check if the source contains some specific patterns.
For example:
for i in range...:
if(i == 2):
.......
I might want to find if the source code contains a pattern just like above: an if statement inside a for loop. I know the expression pattern matching technique, but it does not work for this case.
Does anyone know how to find this kind of pattern matching automatically? Any useful tool?
Use ast.parse().
import ast
code = '''
for i in range(1, 10):
if (i == 2):
print(i)
'''
parsed = ast.parse(code)
for stmt in parsed.body:
if isinstance(stmt, ast.For):
for stmt2 in stmt.body:
if isinstance(stmt2, ast.If):
print("Found if in for")
break
This example is very simple, it only looks for for at the top level of the code, and if at the second level. You should be able to extend it to a recursive solution that searches for nested constructs.
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I apologize because I am coming from Perl and I am new to Python.
The following example looks very long to me:
#!/usr/bin/python
import re
r = re.compile('(?i)m(|[ldf])(\d+)')
m = r.match(text)
if m:
print m.group(2)
In Perl for example it is only one line and it's pretty readable.
#!/usr/bin/perl
print $2 if /m(|[ldf])(\d+)/i
How can I rewrite my Python example to be simpler. If possible to be as light as it is with Perl.
I am planning to write plenty tests and if I want to keep my code readable I would like to avoid consuming lines that will not help people to understand my program. I guess that something like this below would be more readable that my first solution:
r = R()
if r.exec('(?i)m(|[ldf])(\d+)', text): print r.group(2)
if r.exec('(?i)k(|[rhe])(\d{2})', text): print r.group(2)
Unfortunately in this case I have to write a class for this.
The Python way values clarity over brevity, so things are generally going to be more verbose than they are in Perl. That said, the re.compile step is optional.
m = re.match('(?i)m(|[ldf])(\d+)', text)
if m:
print m.group(2)
In Python, assignments are not expressions; they can't be used as values. So there's no way to skip the separate assignment statement (m = ...) or combine it with the if . And if you want to refer to the match object later, you do need an explicit assignment - there's no global implicit state analogous to the Perl $n variables that stores the capture groups automatically.
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Should I create variables just to avoid having long lines of code? For example, in the code below the variable stream_records is only used once after it's set.
stream_records = stream.get_latest_records( num_records_to_correlate ).values('value')
stream_values = [float(record['value']) for record in stream_records]
Should I have done this instead?
stream_values = [float(record['value']) for record in stream.get_latest_records( num_records_to_correlate ).values('value')]
I am trying to optimize for readability. I'd love some opinions on whether it's harder to have to remember lots of variable names or harder to read long lines of code.
EDIT:
Another interesting option to consider for readability (thanks to John Smith Optional):
stream_values = [
float(record['value'])
for record in stream.get_latest_records(
num_records_to_correlate
).values('value')
]
PEP 8 is the style guideline from the beginning of Python, and it recommends that no source lines be longer than 79 characters.
Using a variable for intermediate results also performs a kind of documentation, if you do your variable naming well.
Newlines (carriage return) inside parentheses count as blank.
The same applies to newlines inside brackets, as pointed out by Bas Swinckels.
So you could do something like that:
stream_values = [
float(record['value'])
for record in stream.get_latest_records(
num_records_to_correlate
).values('value')
]
You can also use \ to continue a statement on the following line.
For example:
long_variable_name = object1.attribute1.method1(arg1, arg2, arg3) + \
object2.attribute2.method2(arg1, arg2, arg3)
the first one is definitely easier to read so if there are no performance concerns I would totally go for more variables as long as they have self-explanatory names. it's also way easier to debug if somebody (not you) has to.
The first one is indeed more readable. Creating a variable doesn't cost you a lot here, so you can leave your code with it. Plus, if you are debugging it, it will be much easier to see if the error comes from the call of get_latests_records or from your list comprehension.
However, another way nice way would be to construct your list with the map function:
stream_values = map(lambda x: float(x['value']),
stream.get_latest_records(num_records_to_correlate) \
.values('value')])
The lambda here is necessary, to apply float on the correct value of the dictionary. As you can see, I have limited the number of chars per line to respect the PEP8 convention, which can help to make the code readable too.