Python_Cheat_Sheet.md

Python Cheat Sheet:

Builtin Methods:

• input([prompt]) -> str
  • Read a string from standard input. The trailing newline is stripped. The prompt string, if given, is printed without a trailing newline before reading.
• abs(x) -> number
  • Return the absolute value of x.
• chr(i) -> character
  • Return a string of one character whose ASCII code is the integer i. For example, chr(97) returns the string 'a'. This is the inverse of ord().
• int(x) -> int
  • Convert x to an integer, if possible. A floating point argument will be truncated towards zero.
• len(x) -> int
  • Return the length of the list, tuple, dict, or string x.
• max(iterable) -> object
• max(a, b, c, ...) -> object
  • With a single iterable argument, return its largest item. With two or more arguments, return the largest argument.
• min(iterable) -> object
• min(a, b, c, ...) -> object
  • With a single iterable argument, return its smallest item.
  • With two or more arguments, return the smallest argument.
• ord(c) -> int
  • Given a string of length one, return an integer representing the Unicode code point of the character when the argument is a unicode object, or the value of the byte when the argument is an 8-bit string. For example, ord('a') returns the integer 97
• print(value, ..., sep=' ', end='\n') -> NoneType
  • Prints the values. Optional keyword arguments:
  • sep: string inserted between values, default a space.
  • end: string appended after the last value, default a newline.
• open(name[, mode]) -> file open for reading, writing, or appending
  • Open a file. Legal modes are "r" (read), "w" (write), and "a" (append).
• range([start], stop, [step]) -> list-like-object of int
  • Return the integers starting with start and ending with stop - 1 with step specifying the amount to increment (or decrement).
  • If start is not specified, the list starts at 0. If step is not specified, the values are incremented by 1.

dict:

• D[k] -> object
  • Produce the value associated with the key k in D.
• del D[k]
  • Remove D[k] from D.
• k in d -> bool
  • Produce True if k is a key in D and False otherwise.
• D.get(k) -> object
  • Return D[k] if k in D, otherwise return None.
• D.keys() -> list-like-object of object
  • Return the keys of D.
• D.values() -> list-like-object of object
  • Return the values associated with the keys of D.
• D.items() -> list-like-object of tuple of (object, object)
  • Return the (key, value) pairs of D, as 2-tuples.

file open for reading:

• F = open('workfile', 'r')
  • open a file for reading
• F.close() -> NoneType
  • Close the file.
• F.read() -> str
  • Read until EOF (End Of File) is reached, and return as a string.
• F.readline() -> str
  • Read and return the next line from the file, as a string. Retain newline.
  • Return an empty string at EOF (End Of File).
• F.readlines() -> list of str
  • Return a list of the lines from the file. Each string ends in a newline.
• Loop through file printing every line:

for line in f:
        print line

file open for writing:

• F = open('workfile', 'w')
  • open a file for writing
• F.close() -> NoneType
  • Close the file.
• F.write(x) -> int
  • Write the string x to file F and return the number of characters written.

list:

• x in L -> bool
  • Produce True if x is in L and False otherwise.
• L.append(x) -> NoneType
  • Append x to the end of the list L.
• L.extend(iterable) -> NoneType
  • Extend list L by appending elements from the iterable. Strings and lists are iterables whose elements are characters and list items respectively.
• L.index(value) -> int
  • Return the lowest index of value in L.
• L.insert(index, x) -> NoneType
  • Insert x at position index.
• L.pop() -> object
  • Remove and return the last item from L.
• L.remove(value) -> NoneType
  • Remove the first occurrence of value from L.
• L.reverse() -> NoneType
  • Reverse IN PLACE.
• L.sort() -> NoneType
  • Sort the list in ascending order IN PLACE.

str:

• x in s -> bool
  • Produce True if and only if x is in s.
• str(x) -> str
  • Convert an object into its string representation, if possible.
• S.count(sub[, start[, end]]) -> int
  • Return the number of non-overlapping occurrences of substring sub in string S[start:end].
  • Optional arguments start and end are interpreted as in slice notation.
• S.find(sub[, i]) -> int
  • Return the lowest index in S (starting at S[i], if i is given) where the string sub is found or -1 if sub does not occur in S.
• S.index(sub) -> int
  • Like find but raises an exception if sub does not occur in S.
• S.isalpha() -> bool
  • Return True if and only if all characters in S are alphabetic and there is at least one character in S.
• S.isdigit() -> bool
  • Return True if all characters in S are digits and there is at least one character in S, and False otherwise.
• S.islower() -> bool
  • Return True if and only if all cased characters in S are lowercase and there is at least one cased character in S.
• S.isupper() -> bool
  • Return True if and only if all cased characters in S are uppercase and there is at least one cased character in S.
• str.join(sequence) -> string
  • The method join() returns a string in which the string elements of sequence have been joined by str separator.
• S.lower() -> str
  • Return a copy of the string S converted to lowercase.
• S.lstrip([chars]) -> str
  • Return a copy of the string S with leading whitespace removed.
  • If chars is given and not None, remove characters in chars instead.
• S.replace(old, new) -> str
  • Return a copy of string S with all occurrences of the string old replaced with the string new.
• S.rstrip([chars]) -> str
  • Return a copy of the string S with trailing whitespace removed.
  • If chars is given and not None, remove characters in chars instead.
• S.split([sep]) -> list of str
  • Return a list of the words in S, using string sep as the separator and any whitespace string if sep is not specified.
• S.strip([chars]) -> str
  • Return a copy of S with leading and trailing whitespace removed.
  • If chars is given and not None, remove characters in chars instead.
• S.upper() -> str
  • Return a copy of the string S converted to uppercase.

Some Common Exceptions:

try:
    ...
except SomeException:
    tb = sys.exc_info()[2]
    raise OtherException(...).with_traceback(tb)

• exception TypeError

Raised when an operation or function is applied to an object of inappropriate type. The associated value is a string giving details about the type mismatch.

• exception ValueError

Raised when a built-in operation or function receives an argument that has the right type but an inappropriate value, and the situation is not described by a more precise exception such as IndexError.

• exception ZeroDivisionError

Raised when the second argument of a division or modulo operation is zero. The associated value is a string indicating the type of the operands and the operation.

• exception FileExistsError

Raised when trying to create a file or directory which already exists. Corresponds to errno EEXIST.

• `exception FileNotFoundError'

Raised when a file or directory is requested but doesn’t exist. Corresponds to errno ENOENT.