Lists
list = []
list[i:j] # returns list subset
list[-1] # returns last element
list[:-1] # returns all but the last element
list[i] = val
list[i:j] = otherlist # replace ith to jth-1 elements with otherlist
del list[i:j]
list.append(item)
list.extend(another_list)
list.insert(index, item)
list.pop() # returns and removes last element from the list
list.pop(i) # returns and removes i-th element from the list
list.remove(i) # removes the first item from the list whose value is i
list1 + list2 # combine two list
set(list) # remove duplicate elements from a list
list.reverse() # reverses the elements of the list in-place
list.count(item)
sum(list)
zip(list1, list2) # returns list of tuples with n-th element of both list1 and list2
list.sort() # sorts in-place, returns None
sorted(list) # returns sorted copy of list
",".join(list) # returns a string with list elements seperated by comma
Dict
dict.keys()
dict.values()
"key" in dict # let's say this returns False, then...
dict["key"] # ...this raises KeyError
dict.get("key") # ...this returns None
dict.setdefault("key", 1)
Iteration
for item in ["a", "b", "c"]:
for i in range(4): # 0 to 3
for i in range(4, 8): # 4 to 7
for i in range(1, 9, 2): # 1, 3, 5, 7
for key, val in dict.items():
for index, item in enumerate(list):
String
str[0:4]
len(str)
string.replace("-", " ")
",".join(list)
"hi {0}".format('j')
"hi {name}" # same as "hi {}".format('name')
str.find(",")
str.index(",") # same, but raises IndexError
str.count(",")
str.split(",")
str.lower()
str.upper()
str.title()
str.lstrip()
str.rstrip()
str.strip()
str.islower()
/* escape characters */
>>> 'doesn\'t' # use \' to escape the single quote...
"doesn't"
>>> "doesn't" # ...or use double quotes instead
"doesn't"
>>> '"Yes," they said.'
'"Yes," they said.'
>>> "\"Yes,\" they said."
'"Yes," they said.'
>>> '"Isn\'t," they said.'
'"Isn\'t," they said.'
Casting
int(str)
float(str)
str(int)
str(float)
'string'.encode()
Comprehensions
[fn(i) for i in list] # .map
map(fn, list) # .map, returns iterator
filter(fn, list) # .filter, returns iterator
[fn(i) for i in list if i > 0] # .filter.map
Regex
import re
re.match(r'^[aeiou]', str)
re.sub(r'^[aeiou]', '?', str)
re.sub(r'(xyz)', r'\1', str)
expr = re.compile(r'^...$')
expr.match(...)
expr.sub(...)
File manipulation
Reading
file = open("hello.txt", "r") # open in read mode 'r'
file.close()
print(file.read()) # read the file
print fh.readline() # Reading line by line
Writing (overwrite)
file = open("hello.txt", "w") # open in write mode 'w'
write("Hello World")
text_lines = ["First line", "Second line", "Last line"]
file.writelines(text_lines)
file.close()
Writing (append)
file = open("Hello.txt", "a") # open in append mode
write("Hello World again")
file.close()
Context manager
with open("welcome.txt", "r") as file:
# 'file' refers directly to the "welcome.txt"
data = file.read()
It closes the file automatically, no need for file.close().