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Python Quick Reference
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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) |
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# 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() |
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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): |
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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 |
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# 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(...) |
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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.' |
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