reduce n accumulate
- () around if/for/while is optional
- .split(delimiter) - returns list based on delimeter
- reversed(list) returns listiter object not list itself, so iterate to read values
- append adds individual elm or list(whole), extend adds individual elem of list to target list
- for k, v in d2.items(): print(k, v, sep="->", end=",")
- dict = {x: x ** 2 for x in (2, 3, 4)}
- set : unordered collection of unique element, {}
- for loop for range(for i in list), while uses in operator
- In Set order can change as it is not
- reverse of list is list[::-1]
- lst.sort(reverse=True, key=int) // specify list has integer in form of string
- merge list using extend,append,iterate or itertools.chain
- len(2d_list) or list of list will return number of lists, to know number of item iterate through or recursively these lists, or hetrogenous lists
- type(elem) == list, to check if elem is list
- map(lambda x : x%2 == 1, lst) //lambda applies on each elemnt of lst
Returns all properties and methods of the specified object, without the values obj can be struct function or any other object, or even can be empty
number = [1, 2, 3]
print(dir(number))
print(dir()) # also valid- pylint : install using pip/pip3
- black : install using pip/pip3 // for formatting
- pylance
- bookmarks
Enters space " " after print instead of new line
print("Hello Python 3!!",end=" ")
Print a value (new line) 5 times
print("\n" * 5)
print(f"Let us celebrate {year} {event}") Substitute operator uses {}.format print("first_name {}".format(a))
Prints separator
print(a,b, sep=' : ')
def reuse_fun(message):
print(message)
demo_math()
demo_math()
def pass_func_as_arg_toprint(f, msg):
f(msg)Python has conditional control, recursion, nested loop, break/continue etc
def demo_while_if_else():
print("Given number to compare : ")
given_number = int(input())
while True :
test_number = int(input())
if(test_number < given_number) :
print("Less")
elif(test_number > given_number) :
print("More")
else :
print ("Equal")
break
def factorial(n):
if(n == 1) :
return 1
else :
return n * factorial(n-1)str = "Honesty is the best policy"
list_words = str.split(sep=" ") def demo_slices():
str = "Hello World"
print("First 7 : ",str[0:7]) # Hello W
print("Last 4 : ", str[-4:]) # orld
print("Last 5th to last 1st", str[-5:-1]) # Worl
print("First 3 : ", str[:3]) # Hel
print("third onward : ", str[3:]) # lo World
print("Effectively None : ", str[3:3]) # "" i.e empty stringdef demo_immutable_string():
str = "Hello Python"
#str[0] = 'J' # can not change immutable string
modified_str = 'J' + str[1:]
print(modified_str)def demo_string_func():
str = "Hello Python"
print("Capitalize first letter of each word: ", "hello world".capitalize()) # Hello World
print("length of string is : ", len(str))
print("string in upper case ", str.upper()) # all upper case
print("Count of char c: ", str.count("l", 0, len(str))) # 2
print("lstrip demo:", "44444 Hello World!!!!!!!".lstrip('4')) # all 4 from left till other char starts
print("rstrip demo:", "44444 Hello World!!!!!!!".rstrip('!')) # all ! from the right till other char starts
print("Index of P : ", str.index('P'))
print("Index of Python : ", str.find("Python"))
print("Check if string has e : ", 'e' in str) # True
print("Check if string has a : ", 'a' in str) # False
print("Check if string has 'Python' : ", "Python" in str) # True
first_word = str.split(sep=" ")[0] # Will give list of words, 0 index will give first word of it
if(first_word == "Hello"):
print("First word of string is : ", first_word)
if(first_word < "Python"):
print("String comparison based on alphabtical order")- Element of list can be homogeneous/hetrogeneous
- Can access list items through indexes
- list is mutable so can replace one item by another
- has 'in' and 'not in' operator
- can iterate thorugh range(n), i.e. 0 to n-1
- search item in list using in/not in operator, list.count(item) returns number of itme in list
Most list methods modifies the argument and return None . This is the opposite of the string methods, which return a new string and leave the original alone.
lst = [] # empty list
print(lst)
lst = ["Hello"] * 5 #[ 'Hello', 'Hello', 'Hello', 'Hello', 'Hello']
print(lst)
lst = ["World" for i in range(5)] # ['World', 'World', 'World', 'World', 'World']
print(lst)
list_is_seq = [10,23,45,67]
print ("Element of list can be homogeneous as : ",list_is_seq)
list_hetro = [10,23.5,"No Error",[10,20]]
print ("..OR it can be mixed as : ",list_hetro)
print("Iterate thorugh list element")
for item in list_hetro :
print(item, end = " ")
print("Access list element through Indexes, e.g elem at index 3 is list : ", list_hetro[3])
print("..and its second element is : ", list_hetro[3][1])
list_hetro[2] = [1,2]
print("List is mutable, replacing string at 2 to list : ", list_hetro)
print("Verify if [1,2] is in the list ? : ", [1,2] in list_hetro)
print("Verify if 23.5 is in the list ? : ", 23.5 in list_hetro)
print("Verify if 235 is in the list ? (Should be false): ", 235 in list_hetro)
print("\nIterate thorugh element indexes")
for idx in range(len(list_hetro)) :
print(list_hetro[idx], end = " ")Most list methods modifies the argument and return None . This is the opposite of the string methods, which return a new string and leave the original alone.
-
count(item) gives frequency of 'item' in the list
-
len(list) gives number of items in the list
-
Use reverse, min, max, len
-
del list[id], id can be index or slice syntaxes as well
-
list.remove(item), takes item as argument not index
-
index(item), insert, pop(index), pop(), remove(item), sort, sum
-
append(new_item), extend(new_list)
-
list1 + list to add two list, list * num to multiply list items
-
slice works similar to string
-
append/extend modifies the list whereas + operator creates new list
-
slice also creates a new list
-
new_list = lst[start:stop:step] e.g. reversed_list = lst[::-1]
-
In list remove uses item where as del uses index
-
Delete last element, del lst[-1]
mylist1 = [10,20,30]
mylist1.reverse()
print(mylist1)
mylist = [10,20,30]
mylist.insert(-2,40) # [10, 40, 20, 30] // place at index 2 from last
mylist.insert(1,400) # [10, 400, 40, 20, 30]
print(mylist)
print("Max = ", max(mylist)) #max element
print("Min = ", min(mylist)) #min element
print("Length = ", len(mylist)) # number of element
print("Inded of 20 = ", mylist.index(20))
print("Element at 3 removed : ", mylist.pop(3)) # 20 is popped
print("Last Element : ", mylist.pop()) # 30 is popped
print("Now mylist is : ", mylist)
print("Remove 400 : ")
mylist.remove(400) # removed
list1 = [1,2,3]
list2 = [4,5]
#print("Comparison : ", cmp(list1,list2))
print("Twice the list : ", list2 * 2)
sum_list = list2 + list1
print("sum list (list1 + list2) : ", sum_list)
sum_list.sort()
print("sort list : ", sum_list)
print("sum of sorted list : ", sum(sum_list))
list3 = [6, ["Happy ","Coding", 2.0]]
sum_list = sum_list + list3
print("sum of different lists", sum_list)
list4 = [1,2]
print("Same items get multiplied in case of multiplication, wil print [1,2,1,2] : ", list4 * 2)
# slice works similar to string
list4.append(3) # this does not return list
print("append method updates itself but does not return list : ", list4)
another_list = [4,5]
list4.append(another_list) # will output [1,2,3,[4,5]] not [1,2,3,4,5]
print("append adds whole list not individual elem : ", list4)
lst_to_extend = [6,7]
list4.extend(lst_to_extend) # this does not return list but adds 6, 7 to existing list make list4 = [1, 2, 3, [4, 5], 6, 7]
print(list4)
print("extend function updates itself but does not return list : ", list4.extend(list1))Adding few more
list1 = [1,2,3]
list2 = [4,5]
sum_list = list2 + list1
print("sum list2 + list1 : ", sum_list)
print("Pop top element", sum_list.pop()) # returns top element
print("updated sum_list", sum_list)
del sum_list[1] # slicing can be used
print("Deletes index 1 element(i.e. 5) : ", sum_list)
sum_list.remove(1) #takes element as argument
print("list after removing 1 : ", sum_list)- string to list
- is operator
a = "Hello-Python"
list_a = list(a)
print("list func convert string into list individual chars : ", list_a) #[H,e,l,l.....]
print("string func split converts gives list of words : ", a.split(sep = "-")) # [Hello, Python]
a = "Hello"
b = "Hello"
print("Both points to same string so are equal/identical : ", a is b)
a = [1,2]
b = [1,2]
print("Both are equivalent but not equal/identical : ", a is b)
c = a
print("Aliased, Both are equal/identical : ", c is a)
a[1] = 10
print("As second element of a got modified, c will change too : ", c)Iterate through dict items, separtor and eol customized
for k, v in d2.items():
print(k, v, sep="->", end=",")Dictionaries have keys() values() and items() to get keys, values and key-value pairs. but get list of keys/values do it explicitely e.g. list(dict.keys())
Check if key availabe using
- key in dict
- key in keys
- d[key] is 'KeyError'
dict = sorted(dict) to sort dictionary(on keys) or other containers e.g. list and tuples
Unordered collection of unique element, {}, It provides various set relatd operations
s1 = set("test")
print("s1 (test) -> ", s1) # will outpu {'t', 's', 'e'}
s2 = set("Taste")
print("s2 (Taste) -> ", s2) # will output {'s', 't', 'a', 'e', 'T'}
print("s1 - s2 -> ", s1 - s2) # in s1 but not in s2
print("s2 - s1 -> ", s2 - s1) # in s2 but not in s1
print("s1 | s2 -> ", s1 | s2) # in s1 or s2
print("s1 & s2 -> ", s1 & s2) # both in s1 and s2
print("s1 ^ s2 -> ", s1 ^ s2) # in s1 or s2 but not in bothA tuple is a sequence of values. The values can be any type, and they are indexed by integers, so in that respect tuples are a lot like lists. The important difference is that tuples are immutable.
zip is a built-in function that takes two or more sequences and “zips” them into a list of tuples where each tuple contains one element from each sequence. In Python 3, zip returns an iterator of tuples, but for most purposes, an iterator behaves like a list.
Tuple supports functions such as sort, compare operators(compares begining to end)
empty_tuple = tuple()
print("empty tuple -> ", empty_tuple)
t = "a", "b", "c", "d", "e"
print("tuple from values -> ", t)
# or represent it using (better)
t1 = ("a", "b", "c", "d", "e")
print("tuple from values -> ", t1)
# string to tuple elements
t2 = tuple("abrakadabra")
print("tuple elements from t2 -> ", t2) # it allows duplicates as well
# access method is same as list i.e. 0 based l;
print("t2[0] -> {}\nt2[3:6] -> {}".format(t2[0], t2[3:6]))
# you can not modify tuple elements but can replace tuple
#t3 = t2[0] + t2[3:6] # not working, says can not concatanate
t2 = ("A",) + t2[3:6] # please do notice , after "A"
print("relaced tuple(t2) - > ", t2)It can be read from the code but if you want to update you have to declare locally global x global is not required if it is mutable such as list, dictioanary and sets
Basically used for nested function, need to declare locally if variable is defined in outer nested function. Local/nonlocal variable will get precedence over global one
spam = "temp"
def demo_scope_test():
def do_local():
spam = "local spam"
def do_nonlocal():
nonlocal spam
spam = "nonlocal spam"
def do_global():
global spam
spam = "global spam"
#print(spam) # will print updated value here only
spam = "test spam"
do_local()
print("After local assignment:", spam)
do_nonlocal()
print("After nonlocal assignment:", spam)
do_global()
print("After global assignment:", spam)Outside demo_scope_test, its modified global value that would be available, verify it using
print("In global scope:", spam) # will print "global spam" modified by do_global functionCheck if file is empty
os.stat(path, *, dir_fd=None, follow_symlinks=True)
os.stat(file_path).st_size == 0 to check if file is empty
os.path.getsize(path)
fileStatsObj = os.stat ( filePath )
modificationTime = time.ctime ( fileStatsObj [ stat.ST_MTIME ] )
accessTime = time.ctime ( fileStatsObj [ stat.ST_ATIME ] )
os.path.getmtime(path)
modificationTime = time.strftime('%d/%m/%Y', time.localtime(os.path.getmtime(filePath)))
accessTimesinceEpoc = os.path.getatime(filePath)
accessTime = time.strftime('%Y-%m-%d %H:%M:%S', time.gmtime(accessTimesinceEpoc))
#open file and read first char
one_char = read_obj.read(1)
# if not fetched then file is empty
if not one_char:
return True
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