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Python Articles
Page 845 of 855
Where to put comments in an if...elif..else construct?
You can put comments anywhere in an if...elif...else statement, ie before each of these blocks or within each of these blocks. Note that you cannot put multiline comments before elif and else blocks though, as these comments are actually strings which imply a break in the whole construct. For example,# If check if True: # Another Comment style print("If block") # Else if statement elif False: # Another Comment style print("elif block") # Else else: # Another Comment style print("Else block")This will give the output:If block
Read MoreHow to comment each condition in a multi-line if statement in Python?
You can do this directly if you are surrounding your multiline if statements conditions in a parenthesis. For example,if (cond1 == 'val1' and cond2 == 'val2' and # Some comment cond3 == 'val3' and # Some comment cond4 == 'val4'):However, this is not possible if you try to do this without a parenthesis. For example, the following code will give an error:if cond1 == 'val1' and \ cond2 == 'val2' and \ # Some comment cond3 == 'val3' and \ # Some comment cond4 == 'val4':
Read MoreWhat is python .. ("dot dot") notation syntax?
There is no special .. ("dot dot") notation syntax in python. You can, however, see this in case of floats accessing their properties. For example,f = 1..__truediv__ # or 1..__div__ for python 2 print(f(8))This will give the output:0.125What we have is a float literal without the trailing zero, which we then access the __truediv__ method of. It's not an operator in itself; the first dot is part of the float value, and the second is the dot operator to access the object's properties and methods. This can also be achieved using:>>> f = 1. >>> f 1.0 >>> f.__truediv__
Read MoreWhat is the associativity of Python's ** operator?
From the Python docs:Operators in the same box group left to right (except for comparisons), including tests, which all have the same precedence and chain from left to right — see section Comparisons — and exponentiation, which groups from right to left).So the ** operator(exponentiation) is right to left associative. For example,2 ** 3 ** 4 will be evaluated as: (2 ** (3 ** 4))For example,print(2 ** 3 ** 0)This will give the output:2
Read MoreHow to sort a Python dictionary by datatype?
You can sort a list of dictionaries by values of the dictionary using the sorted function and passing it a lambda that tells which key to use for sorting. For example, A = [{'name':'john', 'age':45}, {'name':'andi', 'age':23}, {'name':'john', 'age':22}, {'name':'paul', 'age':35}, {'name':'john', 'age':21}] new_A = sorted(A, key=lambda x: x['age']) print(new_A)This will give the output:[{'name': 'john', 'age': 21}, {'name': 'john', 'age': 22}, {'name': 'andi', 'age': 23}, {'name': 'paul', 'age': 35}, {'name': 'john', 'age': 45}]You can also sort it in place using the sort function instead of the sorted function. For example, A ...
Read MoreHow to sort a nested Python dictionary?
If you have a dictionary of the following format:{ 'KEY1':{'name':'foo', 'data':1351, 'completed':100}, 'KEY2':{'name':'bar', 'data':1541, 'completed':12}, 'KEY3':{'name':'baz', 'data':58413, 'completed':18} }And you want to sort by the key, completed within each entry, in a ascending order, you can use the sorted function with a lambda that specifies which key to use to sort the data. For example, my_collection = { 'KEY1':{'name':'foo', 'data':1351, 'completed':100}, 'KEY2':{'name':'bar', 'data':1541, 'completed':12}, 'KEY3':{'name':'baz', 'data':58413, 'completed':18} } sorted_keys = sorted(my_collection, key=lambda x: (my_collection[x]['completed'])) print(sorted_keys)This will give the output:['KEY2', 'KEY3', 'KEY1']
Read MoreHow to replace values of a Python dictionary?
You can assign a dictionary value to a variable in Python using the access operator []. For example,Examplemy_dict = { 'foo': 42, 'bar': 12.5 } new_var = my_dict['foo'] print(new_var)OutputThis will give the output −42This syntax can also be used to reassign the value associated with this key. For example,Examplemy_dict = { 'foo': 42, 'bar': 12.5 } my_dict['foo'] = "Hello" print(my_dict['foo'])OutputThis will give the output −Hello
Read MoreHow to use special characters in Python Regular Expression?
From Python documentationNon-special characters match themselves. Special characters don't match themselves −\ Escape special char or start a sequence..Match any char except newline, see re.DOTALL^Match start of the string, see re.MULTILINE $ Match end of the string, see re.MULTILINE[ ]Enclose a set of matchable charsR|S Match either regex R or regex S.()Create capture group, & indicate precedenceAfter '[', enclose a set, the only special chars are −]End the set, if not the 1st char-A range, eg. a-c matches a, b or c^Negate the set only if it is the 1st char Quantifiers (append '?' for non-greedy) ...
Read MoreValid Palindrome in Python
Suppose we have a string with alphanumeric values and symbols. There are lower case and uppercase letters as well. We have to check whether the string is forming a palindrome or not by considering only the lowercase letters (uppercases will be converted into lower case), other symbols like a comma, space will be ignored.Suppose the string is like “A Man, a Plan, a Canal: Panama”, then by considering these rules, it will be “amanaplanacanalpanama”. This is a palindrome.To solve this, follow these steps −define x = “”read each character c in str −if c is lowercase letter or number, then ...
Read MoreHow can I eliminate numbers in a string in Python?
You can create an array to keep track of all non digit characters in a string. Then finally join this array using "".join method. examplemy_str = 'qwerty123asdf32' non_digits = [] for c in my_str: if not c.isdigit(): non_digits.append(c) result = ''.join(non_digits) print(result)OutputThis will give the outputqwertyasdfexampleYou can also achieve this using a python list comprehension in a single line. my_str = 'qwerty123asdf32' result = ''.join([c for c in my_str if not c.isdigit()]) print(result)OutputThis will give the outputqwertyasdf
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