I was checking a project that i have to turn in (it's a battleship game) and for some reason when it runs "through" the section bellow it says "can't assign function call" when it's a copy paste of a piece of just above (with a couple changes) and it gives no error. Do you see the error?
'''
elif y == "v":
if a + 3 > 4:
return "put the boat higher, here it leaves the board"
else:
board(a)(b) = "V"
a = a + 1
board(a)(b) = "V"
a = a + 1
board(a)(b) = "V"
return board
'''
First of all, I highly recommend you to use python 3, read this.
And I don't know what is board, so I will answer for two cases.
board is not a function, nested python list
In this case, just change () to [] to access array.
board is a function
In this case, you're definitely wrong. board() is a function call and will return function result. So, you cannot assign "V" into your function call. This is pretty natural.
Now, check out what is your case and happy coding.
Maybe instead of accessing a matrix with the [] operator you are making calls with (). So try replacing board(a)(b) with board[a][b] but without more information is really hard to tell.
Related
I'm new in stackoverflow and I'd like to make my first question for a problem in this code I've tried to write to learn objects in python.
I'm trying to call the creation of an object through a dictionary.
My purpose is to create an object thanks to a number, for example I have the dictionary newch = {1 : Character.new_dragon(), 2 : Character.new_goblin()} and when I call Player1 = newch[1] it should create a new dragon (#classmethod new_dragon) and assign it to Player1
The problem is that when i run the program, Character.new_dragon() and Character.new_goblin() are called automatically (i put a control print), but when I write "DRAGO" after the request "which player?" the functions aren't called because there isn't the control print
import random
class Character:
def __init__(self,idd,height,weight,att,defe):
self.idd=idd
self.height=height
self.weight=weight
self.att=att
self.defe=defe
#classmethod
def new_goblin(cls):
print('newgoblin')
return cls(1,getr(1,1.5,0.1),getr(40,60,0.5),getr(5,15,1),getr(6,10,1))
#classmethod
def new_dragon(cls):
print('newdrago')
return cls(2,getr(20,30,1),getr(500,2000,5),getr(50,150,3),getr(20,100,3))
def getr(start,stop,step): #returns float
x=random.randint(1, 1000)
random.seed(x)
return random.randint(0, int((stop - start) / step)) * step + start
play={1:'p1', 2:'p2', 3:'p3', 4:'p4'} #dict for players
newch={1:Character.new_dragon(),2:Character.new_goblin()} ############This doesn't work
i=1
while True:
char=input("which player? Drago or Goblin?").upper()
if(char=="DRAGO"):
play[i]=newch[1] #here i try to call Character.new_dragon()
i+=1
break
elif(char=="GOBLIN"):
play[i]=newch[2]
i+=1
break
print("write \'Drago\' or \'Goblin\'")
print(play[1].height, play[1].weight, play[1].att, play[1].defe)
Here's my code, if you could help me, I would be very glad, thanks
The new object is created immediately when you call Character.new_dragon(), and the object is then stored in the dict.
Instead you could not store the object in the dict, but the function that creates it. That function would be Character.new_dragon (without the ()). Then you can call that function when the player selects a character:
play[i]=newch[1]()
Complete code:
import random
class Character:
def __init__(self,idd,height,weight,att,defe):
self.idd=idd
self.height=height
self.weight=weight
self.att=att
self.defe=defe
#classmethod
def new_goblin(cls):
print('newgoblin')
return cls(1,getr(1,1.5,0.1),getr(40,60,0.5),getr(5,15,1),getr(6,10,1))
#classmethod
def new_dragon(cls):
print('newdrago')
return cls(2,getr(20,30,1),getr(500,2000,5),getr(50,150,3),getr(20,100,3))
def getr(start,stop,step): #returns float
x=random.randint(1, 1000)
random.seed(x)
return random.randint(0, int((stop - start) / step)) * step + start
play={1:'p1', 2:'p2', 3:'p3', 4:'p4'} #dict for players
newch={1:Character.new_dragon,2:Character.new_goblin} ############This doesn't work
i=1
while True:
char=input("which player? Drago or Goblin?").upper()
if(char=="DRAGO"):
play[i]=newch[1]() #here i try to call Character.new_dragon()
i+=1
break
elif(char=="GOBLIN"):
play[i]=newch[2]()
i+=1
break
print("write \'Drago\' or \'Goblin\'")
print(play[1].height, play[1].weight, play[1].att, play[1].defe)
This works, however I would not say it is the best coding style. Its hard to judge from only this piece of code, but it might be a better idea to make Drago and Goblin subclasses of the Character class and store the type of those classes in that dictionary.
newch={1:Character.new_dragon(),2:Character.new_goblin()}
As this is written, the new_dragon and new_goblin functions are called when the dictionary is created. This is why you are seeing them both run "automatically" every time you run your program.
If you instead declared the dict like:
newch={1:Character.new_dragon ,2:Character.new_goblin}
And later have something like:
if(char=="DRAGO"):
play[i]=newch[1]()
(note the parenthesis after the newch[1]) you should get what you want.
Incidentally, those break statements aren't necessary. The If/elif/else chain doesn't fall through like a switch statement in other languages.
When you are initialising the dictionary this way:
newch={1:Character.new_dragon(),2:Character.new_goblin()}
You are binding keys (1 and 2) to the return values of the new_dragon and new_goblin functions. You need to bind the functions(without calling them) like so:
newch={1:Character.new_dragon,2:Character.new_goblin}
Notice there are no brackets!
And then, when you create players, you execute those functions like so:
play[i]=newch[1]() Notice here we have brackets!
Additionally, if I may suggest an improvement of the code here:
if(char=="DRAGO"):
play[i]=newch[1]()
i+=1
To avoid the if statement, you can create you mapping with a string:
newch={"DRAGO":Character.new_dragon,"GOBLIN":Character.new_goblin}
And create instances just by calling
play[i]=newch[char]()
To handle errors, you can add just a single if statement checking whether the char string is in the list with dict keys.
I'm having a hard time to understand how to work with functions - I can make then but after that I don't know how to use them. My question is how can I print this code with a function?
string = "Hello"
reverse = string[::-1]
print(reverse)
I tried putting it in a function but I cannot make it print Hello.
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
also tried this
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
Nothing seems to work. I'm having same problem with this as well.
total = 0
def length(words):
for i in words:
total += 1
return total
Functions without a return value
Functions that just take action or do something without returning a value (for example, print).
Functions that don't return a value can be defined like that:
def sayHello():
print "Hello!"
And can be used (called) like that:
sayHello()
And the output will be:
Hello!
Function parameters
A function can also receive parameters (type of variables) from the caller. It's better to demonstrate it with an example.
A function that receives a name and greets this name:
def sayHelloTo(name):
print "Hello", name
It can be called like that:
sayHelloTo("Yotam")
And the output will be:
Hello Yotam
The parameters are the function's input.
Functions with a return value
Other functions, unlike sayHello() or sayHelloTo(name) (that just do something) can return a value. For example, let's make a function that rolls a dice (returns a random number between 1 and 6).
from random import randint
def rollDice():
result = randint(1, 6)
return result
The return keyword just sets the output value of the function and exits the function. An example use of the rollDice function will be:
dice = rollDice()
print "The dice says", dice
When the function hits a return keyword, it finishes and the return value (in our case, the variable result) will be placed instead of the function call. Let's assume randint(1, 6) has produced the number 3.
Result becomes 3.
Result is returned.
Now, instead of the line:
dice = rollDice()
We can treat the line as:
dice = 3
(rollDice() was replaced with 3)
Functions with parameters and a return value
Some functions (for example, math functions) can take inputs AND produce outputs. For example, let's make a function that receives 2 numbers and outputs the greater one.
def max(a,b):
if a > b:
return a
else:
return b
What it does is pretty clear, isn't it? If a is greater, it returns the value of it. Otherwise, returns the value of b.
It can be used like that:
print max(4, 6)
And the output will be:
6
Now, your case
What you want to do is a function that reverses a string. It should take 1 parameter (input) - the string you want to reverse, and output 1 value - the reversed string. This can be accomplished like that:
def reverse_a_string(my_text):
return my_text[::-1]
now you can do something like that:
s = raw_input("Please enter a string to be reversed\n") #input in Python3
r = reverse_a_string(s)
print r
r will contain the reversed value of s, and will be printed.
About your second function - well, I assume that based on this answer you can make it yourself, but comment me if you need assistance with the second one.
Local variables
About your 3rd example:
def reverse_a_string(string):
string = "Hello"
reverse = string[::-1]
print(reverse)
This is something that is really worth delaying and understanding.
the variable reverse is first used inside the function. This makes it a local variable.
This means that the variable is stored in the memory when the function is called, and when it finishes, it is removed. You can say it's lifetime is from when the function is called to when the function is done.
This means that even if you called reverse_a_string(string), you wouln't be able to use the reverse variable outside of the function, because it would be local.
If you do want to pass a value like that, you have to "declare" your variable outside of the function and to use the global keyword, like that:
reverse = "" #This makes reverse a global variable
def reverse_a_string(string):
global reverse #Stating that we are going to use the global variable reverse
reverse = string[::-1]
# Then you can call it like that:
reverse_a_string("Hello")
print reverse
The output will be
olleH
Although it's strongly not recommended to do it in Python, or in any other language.
Once you create a function you must call it. You have created the function reverse_a_string but then you never actually call it. Think about a function as a button that does something everytime it is pushed (or in our case called). If you never push the button then although it has the potential to do something, it never will. In order for the set of instructions to happen we need to push the button (or in our case call the function). So in order for your code to work you first need to define the function then actually call it:
def reverse_a_string():
string="Hello"
reverse = string[::-1]
print reverse
reverse_a_string()
Result: 'olleH'
If you want to pass your own string in to the function so it doesn't just return 'olleH' all the time your code needs to look like such:
def reverse_a_string(stringThatWillBeReversed):
reverse = stringThatWillBeReversed[::-1]
print reverse
reverse_a_string('whateverStringYouWant')
Result: The reverse of the string you entered.
Hope that helps!
I don't know whether you are asking how to define functions in python or something else
If you want to learn python functions, go to http://www.tutorialspoint.com/python/python_functions.htm or just write python tutorial in google, you will get billions of good sites
def reverse_a_string(string):
#function definition
reverse = string[::-1]
print(reverse)
#function call
reverse_a_string("your string")
But you to define function for this, you could simply do
print( string[::-1] )
# defines the 'Reverse a String' function and its arguments
def reverse_a_string():
print(string)
reverse = string[::-1]
print(reverse)
print("Type a string") # asks the user for a string input
string = input() # assigns whatever the user input to the string variable
reverse_a_string() # simply calls the function
for functions, you have to define the function, then simply call it with the function name i.e. funtion()
In my example, I ask for a string, assign that to the variable, and use it within the function. If you just want to print hello (I'm a little unclear from your question) then simply including the print("hello") or w/ variable print(string) will work inside the function as well.
Trying to gain access to this string to test it if it has 3 or more blues "b" inside of it. ---Both test and three_or_more_blues are functions.----- I'm completely lost, any one got an idea? Please change my title if it doesn't fit my question. Not sure really how to ask the question. Thanks!
test(three_or_more_blues, "brrrrrbrrrrrb")
Assuming test is a function that takes a function and a string as paramters, and three_or_more_blues is a function that returns true if its string parameter has 3 or more 'b' characters, then
def test(func, str):
if func(str):
# do something with str
test(three_or_more_blues, "brrrrrbrrrrrb")
You could use .count().
sentence = 'brrrrrbrrrrrb'
amount = sentence.count('b')
print(amount)
And then you could use a loop to calculate your next step.
if (amount >= 3):
# Do something
I am not sure if I understand you correctly - you are asking how to pass the string 'brrrrrbrrrrrb' to the three_or_more_blues function?
If that is the case, than you just simply pass it when you call the three_or_more_blues function like this:
def test(func, some_string):
func(some_string) # here you call the passed function
# if three_or_more_blues would look like this:
def three_or_more_blues(some_string):
print "Yes, 3 or more b's" if some_string.count('b') >= 0 else "No"
# you would get this from your function call
test(three_or_more_blues, "brrrrrbrrrrrb") # prints: "Yes, 3 or more b's"
I am still new to Python and have been reviewing the following code not written by me.
Could someone please explain how the first instance of the variable "clean" is able to be be called in the check_arguments function? It seems to me as though it is calling an as yet undefined variable. The code works but shouldn't that call to "clean" produce an error?
To be clear the bit I am referring to is this.
def check_arguments(ages):
clean, ages_list = parse_ages_argument(ages)
The full code is as follows...
def check_arguments(ages):
clean, ages_list = parse_ages_argument(ages)
if clean != True:
print('invalid ages: %s') % ages
return ages_list
def parse_ages_argument(ages):
clean = True
ages_list = []
ages_string_list = ages.split(',')
for age_string in ages_string_list:
if age_string.isdigit() != True:
clean = False
break
for age_string in ages_string_list:
try:
ages_list.append(int(age_string))
except ValueError:
clean = False
break
ages_list.sort(reverse=True)
return clean, ages_list
ages_list = check_arguments('1,2,3')
print(ages_list)
Python doesn't have a comma operator. What you are seeing is sequence unpacking.
>>> a, b = 1, 2
>>> print a, b
1 2
how the first instance of the variable "clean" is able to be be called in the check_arguments function?
This is a nonsensical thing to ask in the first place, since variables aren't called; functions are. Further, "instance" normally means "a value that is of some class type", not "occurrence of the thing in question in the code listing".
That said: the line of code in question does not use an undefined variable clean. It defines the variable clean (and ages_list at the same time). parse_ages_argument returns two values (as you can see by examining its return statement). The two returned values are assigned to the two variables, respectively.
A really simple question, and I'm sure I knew it but must have forgotten
When running this code:
x = 0
def run_5():
print "5 minutes later"
x += 5
print x, "minutes since start"
run_5()
print x
I get x isn't defined. How can I have x used in the function and effected outside of it?
Just return a value ?
x = 0
def run_5():
print "5 minutes later"
x += 5
return x
x=run_5()
print x
Put global x at the start of the function.
However, you should consider if you really need this - it would be better to return the value from the function.
Just to make sure, the x that is not defined is the one on line 4, not the one on the last line.
The x outside the function is still there and unaffected. It's the one inside that can't have anything added to it because, as far as Python is concerned, it does not exist when you try to apply the += operator to it.
I think you need to define a variable outside the function, if you want to assign it a return value from the function.
The name of the variable can be different than the name in function as it is just holding it