I have been converting a Qt/C++ widget code into PyQt4+Python3. I have a QFileSystemModel defined and the items it returns have "data" with the filename as type "str". (This is of type QString in Qt/C++ or Python2x).
I have to search for a filter based on QRegEx. In Qt/C++ and Python2x this is achieved by QString.contains(QRegEx).
I found that QString has been removed in Python3. Since now in Python3 everything is now of type "str", how can i implement the old method QString.contains(QRegEx)?
Thanks,
Kodanda
For string mainipulation, Python is generally superior to anything Qt has to offer (particularly when it comes to regular expressions).
But if you must use QRegExp:
# test whether string contains pattern
if QRegExp(pattern).indexIn(string) != -1:
print('found')
Python:
if re.search(pattern, string):
print('found')
Related
I want to use f-string with my string variable, not with string defined with a string literal, "...".
Here is my code:
name=["deep","mahesh","nirbhay"]
user_input = r"certi_{element}" # this string I ask from user
for element in name:
print(f"{user_input}")
This code gives output:
certi_{element}
certi_{element}
certi_{element}
But I want:
certi_{deep}
certi_{mahesh}
certi_{nirbhay}
How can I do this?
f"..." strings are great when interpolating expression results into a literal, but you don't have a literal, you have a template string in a separate variable.
You can use str.format() to apply values to that template:
name=["deep","mahesh","nirbhay"]
user_input = "certi_{element}" # this string i ask from user
for value in name:
print(user_input.format(element=value))
String formatting placeholders that use names (such as {element}) are not variables. You assign a value for each name in the keyword arguments of the str.format() call instead. In the above example, element=value passes in the value of the value variable to fill in the placeholder with the element.
Unlike f-strings, the {...} placeholders are not expressions and you can't use arbitrary Python expressions in the template. This is a good thing, you wouldn't want end-users to be able to execute arbitrary Python code in your program. See the Format String Syntax documenation for details.
You can pass in any number of names; the string template doesn't have to use any of them. If you combine str.format() with the **mapping call convention, you can use any dictionary as the source of values:
template_values = {
'name': 'Ford Prefect',
'number': 42,
'company': 'Sirius Cybernetics Corporation',
'element': 'Improbability Drive',
}
print(user_input.format(**template_values)
The above would let a user use any of the names in template_values in their template, any number of times they like.
While you can use locals() and globals() to produce dictionaries mapping variable names to values, I'd not recommend that approach. Use a dedicated namespace like the above to limit what names are available, and document those names for your end-users.
If you define:
def fstr(template):
return eval(f"f'{template}'")
Then you can do:
name=["deep","mahesh","nirbhay"]
user_input = r"certi_{element}" # this string i ask from user
for element in name:
print(fstr(user_input))
Which gives as output:
certi_deep
certi_mahesh
certi_nirbhay
But be aware that users can use expressions in the template, like e.g.:
import os # assume you have used os somewhere
user_input = r"certi_{os.environ}"
for element in name:
print(fstr(user_input))
You definitely don't want this!
Therefore, a much safer option is to define:
def fstr(template, **kwargs):
return eval(f"f'{template}'", kwargs)
Arbitrary code is no longer possible, but users can still use string expressions like:
user_input = r"certi_{element.upper()*2}"
for element in name:
print(fstr(user_input, element=element))
Gives as output:
certi_DEEPDEEP
certi_MAHESHMAHESH
certi_NIRBHAYNIRBHAY
Which may be desired in some cases.
If you want the user to have access to your namespace, you can do that, but the consequences are entirely on you. Instead of using f-strings, you can use the format method to interpolate dynamically, with a very similar syntax.
If you want the user to have access to only a small number of specific variables, you can do something like
name=["deep", "mahesh", "nirbhay"]
user_input = "certi_{element}" # this string i ask from user
for element in name:
my_str = user_input.format(element=element)
print(f"{my_str}")
You can of course rename the key that the user inputs vs the variable name that you use:
my_str = user_input.format(element=some_other_variable)
And you can just go and let the user have access to your whole namespace (or at least most of it). Please don't do this, but be aware that you can:
my_str = user_input.format(**locals(), **globals())
The reason that I went with print(f'{my_str}') instead of print(my_str) is to avoid the situation where literal braces get treated as further, erroneous expansions. For example, user_input = 'certi_{{{element}}}'
I was looking for something similar with your problem.
I came across this other question's answer: https://stackoverflow.com/a/54780825/7381826
Using that idea, I tweaked your code:
user_input = r"certi_"
for element in name:
print(f"{user_input}{element}")
And I got this result:
certi_deep
certi_mahesh
certi_nirbhay
If you would rather stick to the layout in the question, then this final edit did the trick:
for element in name:
print(f"{user_input}" "{" f"{element}" "}")
Reading the security concerns of all other questions, I don't think this alternative has serious security risks because it does not define a new function with eval().
I am no security expert so please do correct me if I am wrong.
This is what you’re looking for. Just change the last line of your original code:
name=["deep","mahesh","nirbhay"]
user_input = "certi_{element}" # this string I ask from user
for element in name:
print(eval("f'" + f"{user_input}" + "'"))
I am trying to create a program which checks to see if words entered (when run) are in an array. I would like to use a loop for this.
I have created a list of words and tried a for loop however the code is proving to be erroneous.
def Mylist():
Mylist= [Toyota,BMW,Pontiac,Cadillac,Ford,Opel]
Search=input("Enter a word")
Mylist[1]="Toyota"
for loop in range (1,6):
if Mylist[loop]==Search:
print("found")
break
I have repeated line 4 for the other car manufacturers.
TypeError: 'function' object does not support item assignment
First, here some recommendations to start:
Indentation in Python is IMPORTANT, be careful to have the right indentation. You must take special care when posting code here in SO so your code does not look like complete gibberish.
You should read Naming conventions. TL;DR we use snake_case for naming functions and variables.
If you are not using an IDE (such as PyCharm) to program, or something intelligent that shows the information on functions, you should always check out the documentation (it is beautiful).
Check out the difference between "Toyota" and Toyota. The first one has quotes, it is a string (i.e. chain of characters), it is a primitive type such as integer and boolean; the second is a token that is to be evaluated, it has to be defined before, such as variables, functions and classes.
Search in the docs if there is an in-built function that already does the job you want.
Check out return values in functions. Functions evaluate to None when you do not explicit a return value.
Now to your question. As some people pointed out, there is the in keyword that does exactly what you want.
CAR_BRANDS= ["Toyota", "BMW", "Pontiac", "Cadillac", "Ford","Opel"]
def check_car():
word = input("Enter a word: ")
if word in CAR_BRANDS:
print("found")
return True
print("not found")
return False
If you don't care about the print you can just do return word in CAR_BRANDS
If you actually want to challenge yourself to write the logic, you were right in choosing a for-loop to iterate over the list.
Index in Python starts from 0, and that range does not give you all the indexes to iterate over your list, you are missing the 0 index. Also, we don't like magic numbers, instead of hard-coding the length of your list of car brands, better compute the length!
for i in range(len(CAR_BRANDS)):
if CAR_BRANDS[i] == word:
print("found")
But even better you can directly iterate over the items in your list, no need to do the range, which will give you something like:
CAR_BRANDS= ["Toyota", "BMW", "Pontiac", "Cadillac", "Ford","Opel"]
def check_car():
word = input("Enter a word: ")
for brand in CAR_BRANDS:
if brand == word:
print("found")
return True
print("not found")
return False
If you have any more questions, do not hesitate! Happy coding.
I am trying to do some very basic string formatting and I got immediately stuck.
What is wrong with this code?
import strutils
import parseopt2
for kind, key, val in getopt():
echo "$1 $2 $3" % [kind, key, val]
I get Error: type mismatch: got (TaintedString) but expected 'CmdLineKind = enum' but I don't understand how shall I fix it.
The problem here is that Nim's formatting operator % expects an array of objects with the same type. Since the first element of the array here has the CmdLineKind enum type, the compiler expects the rest of the elements to have the same type. Obviously, what you really want is all of the elements to have the string type and you can enforce this by explicitly converting the first paramter to string (with the $ operator).
import strutils
import parseopt2
for kind, key, val in getopt():
echo "$1 $2 $3" % [$kind, key, val]
In case, you are also wondering what is this TaintedString type appearing in the error message, this is a special type indicating a non-validated external input to the program. Since non-validated input data poses a security risk, the language supports a special "taint mode", which helps you keep track of where the inputs may need validation. This mode is inspired by a similar set of features available in the Perl programming language:
http://docstore.mik.ua/orelly/linux/cgi/ch08_04.htm
If you use the strformat Nim-inbuilt library, the same code snippet can be more concise:
import parseopt # parseopt2 has been deprecated!
import strformat
for kind, key, val in getopt():
echo fmt"{kind} {key} {val}"
Also note that parseopt replaces the deprecated parseopt2 library, at least as of today on Nim 0.19.2.
I want to write a list of strings to a binary file. Suppose I have a list of strings mylist? Assume the items of the list has a '\t' at the end, except the last one has a '\n' at the end (to help me, recover the data back). Example: ['test\t', 'test1\t', 'test2\t', 'testl\n']
For a numpy ndarray, I found the following script that worked (got it from here numpy to r converter):
binfile = open('myfile.bin','wb')
for i in range(mynpdata.shape[1]):
binfile.write(struct.pack('%id' % mynpdata.shape[0], *mynpdata[:,i]))
binfile.close()
Does binfile.write automatically parses all the data if variable has * in front it (such in the *mynpdata[:,i] example above)? Would this work with a list of integers in the same way (e.g. *myIntList)?
How can I do the same with a list of string?
I tried it on a single string using (which I found somewhere on the net):
oneString = 'test'
oneStringByte = bytes(oneString,'utf-8')
struct.pack('I%ds' % (len(oneString),), len(oneString), oneString)
but I couldn't understand why is the % within 'I%ds' above replaced by (len(oneString),) instead of len(oneString) like the ndarray example AND also why is both len(oneString) and oneString passed?
Can someone help me with writing a list of string (if necessary, assuming it is written to the same binary file where I wrote out the ndarray) ?
There's no need for struct. Simply join the strings and encode them using either a specified or an assumed text encoding in order to turn them into bytes.
''.join(L).encode('utf-8')
I'm using junit in scala to compare string output from my scala code. Something like :
val expected = """<Destination id="0" type="EMAIL">
<Address>
me#test.com
</Address>
<TimeZone>
US/Eastern
</TimeZone>
<Message>
</Message>
</Destination>
"""
val actual = getTextToLog()
info(" actual = " + actual)
assert(expected == actual)
The issue is that for some strings, assertions like :
assert(expected == actual)
work and for some they strings they dont. Even when I copy actual (logged to Eclipse console) from Eclipse console and paste it into expected just to be sure , the assertion still fails.
What am I missing?
OK, since this turns out to be a whitespace issues, you should sanitise the two strings before comparing them. Look at the RichString methods like .lines, for example, which might let you create a line-ending or whitespace-agnostic comparison method.
Here is one naive way of doing this with implicit conversions:
import scala.language.implicitConversions
object WhiteSpace {
implicit def strToWhiteSpace(s: String) = new WhiteSpace(s)
}
class WhiteSpace(val s: String) {
def `~==` (other: String) = s.lines.toList == other.lines.toList
}
which allows
import WhiteSpace._
assert(expected ~== actual)
Or you could extend the appropriate jutils class to add an agnostic version of assertEquals.
Note that this comparison deconstructs both strings in the same way. This is much safer than sending one of them on a round-trip conversion.
Whitespace/crlf issues are so common that there's no point fighting it by trying to stop the mismatches; just do agnostic comparisons.